Let's see, my first completed run looked something like this:
Human Warrior PC: Templar/Champion - I think I did it in that order. Anyway, she was Sword and Shiled and made a hell of a primary tank, in my opinion.
Wynn: Spirit Healer - I don't think I ever gave her another specialization. She was focused on buffing, healing, and a little bit of damage support. I had to control her manually half the time because her tactics made her burn through mana and chug potions like they were soda.
Lelianna: Bard/Duelist - Pretty sure that's what it was. She was my archer/unlocky things support.
Alistair: Templar/... maybe Berzerker? - Al was mostly a support tank/extra melee, as he lagged way behind my PC's development. Sometimes I swapped him out for Oghren when I got him, but he was there most of the time.
Needless to say, that was my goody-two shoes game, as well.
My most recent game, it wasn't really that different.
Elf Mage: Spirit Healer/Arcane Warrior - The full creation line (I'm going for the acheivements, don't hurt me). He was actually kindof fun to play, keeping the tougher baddies out of the fight until the trash mobs were delt with. I ended up putting him into melee near the end of the game once he got all the AW talents, though looking back, it wasn't the greatest idea.
Alistair: Alistair was my main tank up until the end of the game when something happened that I can't reveal in the no spoiler forum. However, I'll say that it wasn't worth it.
Lelianna: Bard/Ranger - Ranged DPS again, I built her much more to my satisfaction this time, and she was still awesome at spotting and disabling traps.
Zeveran: Assassin/Duelist - Dual Weild stabby death. I brought Zev along since he was my PC's Love Intrest, and he was surprisingly more moral than I expected him to be, so it worked out.
I tend to select my parties based on a combination of factors between the kind of character I'm roleplaying, what class/spec I'm using, and who the LI is. Not sure how my next playthrough is gonna go. I might try out Shale as a tank. Or a respeced Sten, using the respec mod.