I played a mage about halfway through the game last January. Picked it back up again last month and finished with a rogue, now working on another mage.
Alistair is good for a tank, Leliana for ranged/chests/traps. I've been switching it up between Dog and Wynne/Morrigan for my last slot. Two mages is definitely nice, but I've also done fine with only my PC mage--have basic healing, but let Alistair lean on pots so I can disable/damage. Leliana and Dog don't usually draw enough aggro to get into much trouble.
You should definitely check out the community mods, some of them are very handy. Advanced Tactics gives more options for the Tactics menu (I'd even recommend using it 1st time through). Advanced Party is nice for subsequent playthroughs. It resets any character that joins your party to base stats, and allows you to use all of their stat, talent, and skill points yourself. I like being able to set up Morrigan and Wynne to have different spell sets in different games (gives more opportunity to try out different spell lines). In my current game, I changed Alistair to a 2-Hander instead of SnS to try those skills out. Does get annoying having to spec temporary members in the origin stories, Daveth and Jory (but at least you can give Daveth Lock-picking), and Tower of Ishal.
This is a mod list with short descriptions and links (easier to browse than bioware site):
http://code.google.com/p/dragon-age-...yers#Bug_Fixes