More major glyphs
Glyph of Pillar of Frost continues as it has been. Personally, I've never been able to justify the whole being rooted in place thing, but if you really hate being feared or find yourself in a situation where being feared could mean running headlong into death, this might be worth it for your frost death knight.
Glyph of Shifting Presences was, at one point, looking like a must-use glyph for DPS death knights especially. However, with presences balanced much, much better as we head into the live servers, I don't expect this to be as useful as once appeared to be. Ghostcrawler has said that he'd prefer death knights don't have to presence-weave to maximize their DPS, so I wouldn't expect this to see much use, and if it does, I'd expect Blizzard to remedy it within a patch or two.
Glyph of Strangulate will probably continue to prove useful against healers and other casters. Two more seconds could be just the thing you need to keep a healer locked down long enough to kill him or his teammates.
Glyph of Unholy Command remains a compelling choice for leveling, allowing you to chain pull quest mobs and beat other players to the punch. I would recommend trying to find a space for this in your leveling build or even your daily grinding build. Although its usefulness will drop off when you hit max level, you may even find it useful if you're in a chain pulling or timed challenge dungeon running group.
Glyph of Unholy Frenzy is probably the closest unholy gets to a "mandatory" glyph choice. If you're a raider, you'll want to be able to give out Unholy Frenzy on the regular, and making it free of the health cost makes it easier and more intuitive to give out.
Glyph of Vampiric Blood is an easy choice for a raid tank to make. Chances are, you're going to be getting healed so much that the extra 15% healing will more than make up for losing the initial heal. Just be sure you can compensate with another cooldown when you're low health.
Glyph of Army of the Dead Army of the Dead has received a few buffs in the Mists beta, mostly due to fixes to other pet scaling issues. That said, it's still not an amazing source of damage, and it's still borderline doubtful that it does enough damage to justify interrupting your damage rotation. Of course, if you pre-cast it right before pulling a boss, it's still likely to be a net increase in your damage. With that in mind, Glyph of Army of the Dead might be useful. Your main choice in taking this glyph is whether you want to remove most of guesswork in casting the spell for DPS or whether you want to keep the taunt in as a possible wipe prevention measure.
Glyph of Corpse Explosion brings back one of the most beloved old death knight abilities. Unfortunately, this glyph is entirely cosmetic. It will explode corpses and leave behind the requisite pile of gore but do no damage in the process. In short, it's good for a bit of nostalgia and may make looting a mob slightly easier or clearing a crowded battlefield, but don't sweat it if you can't fit it into your glyph scheme.
Glyph of Death Gate is mentioned here only for completeness' sake. I suppose if you're insanely impatient the cast time reduction might be worth it, but I wouldn't waste the slot.
Glyph of Death's Embrace continues to be a valid possibility for an unholy death knight who needs to keep his minion standing through long, tough fights whether in PvE or PvP. While it's not mandatory, keeping more of your runic power so you can use it for other things once your ghoul is healed is a net gain. Frost and blood death knights probably won't keep their ghoul up long enough to need to bother.
Glyph of Foul Menagerie, Glyph of the Geist, and Glyph of Horn of Winter round out your cosmetic glyphs. Taking them is purely up to you, as they offer no gameplay benefits, but I know I will be using Glyph of the Geist no matter what my spec. Those dudes look so cool.
Glyph of Path of Frost can definitely be useful if you're doing a little exploring, especially since you won't be able to fly in Pandaria until you hit max level and spend some gold. Of course, you have to remember to actually cast Path of Frost for it to be useful. I'd consider it a valid leveling glyph though, at the least.
Glyph of Resilient Grip might be considered useful for leveling, but I doubt you'll find many mobs that actively resist your Death Grip. I'd personally rather use it for other pursuits.
Glyph of Tranquil Grip is one of those glyphs you'll probably just wish you could force newbie DPS death knights to take. At the same time, Death Grip is now the only DPS emergency taunt, since Dark Command has gone blood-only in Mists. In the end, you may want to skip taking this glyph in order to have an emergency way to peel a mob off your healer. On the other hand, if you're the type of DPS death knight who reflexively hits your death grip button without meaning to, this glyph may make your tank slightly less annoyed with you.
Too Long; Didn't Read version
For those with short attention spans, the main takeaway is this:
For better or for worse, there's not much else in the way of mandatory glyphs out there at the moment. So for now, study up on what they do, and when patch 5.0 drops, be ready to make some choices.
Learn the ropes of endgame play with WoW Insider's DK 101 guide. Make yourself invaluable to your raid group with Mind Freeze and other interrupts, gear up with pre-heroic DPS gear or pre-heroic tank gear, and plot your path to tier 11/valor point DPS gear.