When I get some time, I'll have to take a look around for strat guides for these encounters to perhaps add some tips of my own. Please note group compositions, because strats can vary greatly depending on what classes you have. I have a paladin tank and a sole priest healer; my strats are based on having these.

I agree that UK was rather easy to farm for the epics (great caster ring), so long as you don't need to fight the first boss. If you don't really need the first boss, just skip him; run past him hugging the right wall. I was there mainly for the epic drops, and not so much the emblems, at least initially. If you want to take him on, there's already threads discussing that on here.

Second boss(es), I just tear down the caster right away, then just focus on the warrior. The caster will shoot bolts randomly at people whether he is alive or dead, so I don't see the point to taking them both down at the same time, really. Just do NOT kill the warrior first, as you cannot hold agg on him when he's dead (unless you plan to drop the caster within about 10 seconds of him).

Last boss, I line up all my guys about 15 yards apart (anything over 10 yards is enough, this is to avoid the whirling axe AoE in phase 2) and pull the boss into range of them. Stop all casting at the roar (I just jump with all toons), and move the tank away when the slam is coming. Watch for the whirling axe he throws at a random person and get a big heal off on them (or two) after it lands. Save all cooldowns for the second phase when he is revived by the valkyrie. My strat is blow all cooldowns right at the start of phase 2 (tank loses no aggro from phase 1 -> phase 2, so blast away) to take him down ASAP, but it's hardly necessary to do it this way.

And just to add my strat for Ionar, since I have a priest (groups heals), I just spread my toons out into a 5-point star in the large hallway at the base of his stairs and pull him there so no "spider" can touch more than one person at a time, and pretty much only use group heals until he forms up again. Use a big heal if you get a few all stacked up on one person. With a priest and good spacing, there's no need to even move. Just don't be overzealous on the healing or you might run out of mana too fast. EDIT: How could I forget to mention Nature Resist Totem, too.

CoS, just go nice and easy. First run is more about learning the instance than anything. The infinite dragonflight was the biggest pain for me. For the upstairs hallway, I wait for Arthas to go in and then I just pull them off of him right away (he's a bad tank), rather than following him into the hall and having 2 enemies in front of me and 2 behind me.