With 4.0 around the corner, a number of changes are going to hit us in the behind, causing us to reconsider how we play the game.  With the new glyph system included in the changes, mages have a number of new things to consider to get our stuff back in order and get used to the changes before cataclysm.  With the new system, once you buy a glyph you have it available forever and can switch back and forth between them freely.  Sure this is going to put a big dent in the pocket of the inscriptionists, but to be honest, how often did you flip glyphs around as a mage anyway?  Windsoar has posted a lovely compilation of all the new glyphs come 4.0 on her blog.  If you use the nice little table of contents she has on the top, you can skip down and peruse the mage glyphs.

• Prime Glyphs:  There are 5 viable prime glyphs for this spec, 2 of which I would consider the most effective for a flat dps increase and 3 that are more or less a personal choice.  The two I would say are best choices are Glyph of Arcane Blast and Glyph of Arcane Missiles.  With the changes to Arcane Blast's damage increase only applying to the spell itself and not others in the tree, your rotation will change slightly to include more Blast spamming than the 4 stacks and missile proc we were doing before.  I imagine it won't change that much as spamming Arcane Blast is a good way to run out of mana fast, so you'll want those missiles in there periodically to slow your mana drain.  This is where the second glyph comes in, increasing the crit chance of those missiles.  This goes hand in hand with the talents Master of Elements and Piercing Ice, not to mention Focus Magic.  Glyph of Arcane Barrage is a rather lack luster damage increase to a rarely used spell.  Should it come into play more in the rotation, it might be useful, but I don't suspect it will.  Glyph of Mage Armor and Glyph of Molten Armor are the last two glyphs that would benefit this spec.  The only real reason to take the Mage Armor regen increase is if you're burning through mana quicker than you can use your cooldowns to regain it.  Glyph of Molten armor is going to give you a better flat DPS increase.
• Major Glyphs:  The only real essential glyph I can see in this list is Glyph of Arcane Power.  This glyph is a huge help for cooldown management.  Currently when an arcane mage starts a boss fight or is looking for burst in PVP, they use Mirror Image, Arcane Power, and Icy Veins all at the same time.  With the talent changes coming in 4.0, Icy Veins will be a purely frost talent and will be removed from our cooldown buttons leaving only Mirror Image and Arcane Power.  I suspect our cooldown management will change so that instead of blowing everything at once, we'll start using Mirror Image through it's duration and then hitting Arcane Power and using it again, similar to how Marksman hunters use their readiness ability to maximize their Quick Shots.  Following the first use of these cooldowns, I suspect we'll either work off the 2 min cooldown of Arcane Power or repeat the process after the 3 min cooldown of Mirror Image is up.  The reduced cooldown to Blink and Mana Shield are nice perks, but not quite as useful for PVE.  Now we find ourselves with two more slots for major glyphs and a few available choices for the spec, all of them seem rather a personal choice to me.  Glyph of Blink basically gives you a larger movement range and isn't a DPS increase at all, making it fairly useless.  Glyph of Evocation turns your big mana regen mechanic into a heal as well, which is frankly more useful in soloing and PVP than in a raiding or group environment as ideally, the tank is the one taking the damage and not the mage.  Glyph of Frost Nova gives you a bit more damage on a spell that's not a regular part of our rotation and would be used only in emergency situations.  Glyph of Ice Block might be useful in emergency situations as well, just in case you happen to pull aggro or your CC breaks.  Should that be the case, it might be a good choice in conjunction with Glyph of Frost Nova.  Glyph of Invisibility gives you a flat movement speed increase while invisible, making it moderately useful for aggro dump situations when you're standing in fire.  Glyph of Mana Shield decreases the cooldown on a spell I find myself rarely using in PVE group/raid situations, so might be better for soloing or PVP, unless you find yourself using it a lot for Incanter's Absorption.  Glyph of Polymorph is going to be useful in dungeons where we'll actually have to CC again for a change... now when that stupid rogue poisons your sheep because he's tab targeting and not paying attention, you can re-sheep and not worry about it.  Lastly we have Glyph of Slow, which increases the range of Slow so that it's equal to that of our Arcane Blast, meaning if we're going to apply it to something to kite, we don't have to move in any further.  With Nether Vortex, this may or may not be necessary, but that remains to be seen.
• Minor Glyphs:  As before, the minor glyphs are only there for small changes that don't really do anything for your damage.  This remains the same after the change.  They're all based on personal preference.  Glyph of Arcane Brilliance and Glyph of Conjuring decrease mana costs in generally out of combat situations.  Glyph of Armors saves you having to recast your armors that often, though I prefer to leave mine on the same timer as Focus Magic so I can keep an eye on it's up time as well.  Glyph of Mirror Image may actually prove rather useful in PVE if the damage bonuses from your particular tree apply to those mirrors.  Otherwise it'll just make you harder to be found in PVP.  Glyph of Slow Fall removes the reagent requirement for the spell and Glyph of the Monkey and Penguin affect the appearance of your Polymorph. 

• Prime Glyphs:  There are 4 obvious choices for these glyphs that increase the damage of major part of the new frost rotation which consists of Frostbolt spam, Fingers of Frost procs with Deep Freeze and Ice Lance, and Brain Freeze procs with Frostfire Bolt.  Any of the following choices is a good one as far as I'm concerned and you can pick any of the 3:  Glyph of Deep Freeze, Glyph of Frost Bolt, Glyph of Frostfire, and Glyph of Ice Lance.  Glyph of Cone of Cold might be considered as well, but due to it's very small range, I don't see it being that useful.  Glyph of Mage Armor and Molten Armor are also available, but not optimal choices. 
• Major Glyphs:  Glyph of Frost Nova is the big glyph you want here.  Frost Nova is going to be a big part of the rotation to maximize Deep Freeze procs along with your Perma-elemental's Freeze and Fingers of Frost.  While the range makes it less desirable to use, it's still a part of maximizing your dps in most situations.  Glyph of Ice Block might also be useful for aggro dumps.  Glyph of Ice Barrier might also be useful if there's a damage aura present, but also in PVP.  Glyph of Icy Veins also has limited usefulness.  The remaining glyphs that apply to frost (Glyph of Blink, Evocation, Invisibility, and Polymorph) are all situation and limited in their usefulness.  I would consider them only if none of the others proved useful.
• Minor Glyphs:  See Arcane.

• Prime Glyphs:  The big glyphs to take in this tree are Glyph of Fireball, Pyroblast, and Living Bomb.  All three of these are going to be regularly used in your rotation and the flat damage increase is a big plus.  The two armor glyphs previously mentioned could be used as well, but I doubt they'd be quite as useful.
• Major Glyphs:  Unlike Frost and Arcane, there's no real obvious must-have glyph here, except perhaps Glyph of Dragon's Breath for AOE situations.  Glyph of Blast Wave is more or less for PVP or kiting purposes, but certainly not essential.  The rest of the glyphs are again situational.
• Minor Glyphs:  See Arcane again.

I'm looking forward to 4.0 hitting the live servers.  I took some time to test it on the PTR in all three specs and I have to say I'm intrigued about the changes.  I'm also very pleased that Blizzard has tried to make all 3 specs viable for mages in all situations, though I know we'll see some obvious forerunners on the DPS front.  See you in 4.0!