Given that he's got the "evil" chops and doesn't mind working underneath a tone of makeup (and see
Hannibal if you don't believe me), I would nominate Gary Oldman to play Raistlin. The fact that he's much too old, technically, works in his favour, since Raistlin's appearance will distract from that anyway, and he
is meant to have had his health utterly shattered. I can easily imagine Oldman in the part. He also doesn't suffer quite as much from the "too damn sexy to play the part" factor that James Marsters does; sure, he's a good-looking guy but it's easy to hide, and there is at least one woman who finds Raistlin attractive anyway.
James Purefoy would, I think, make a fine Tanis with the right beard and hair colour. He has very expressive eyes and I think he could convey Tanis' inner conflict very well.
Those are the two who really require the best actors, since they carry the story. Of course, the actor playing Sturm needs to match up to their standards, but his part is smaller. You could easily go with an unknown or a smaller TV actor for that role. Perhaps Nathan Fillion, actually; with the right accent and a good mustache I can see it.
For Tasslehoff, you need someone who can play "young" but doesn't look it - since kender have lined faces, a child actor wouldn't do. I'd recommend Aron Eisenberg, who played Nog on
Deep Space Nine. He can do a highish voice and his small stature is perfect.
Flint can be anyone physically right for the part, as long as they're well-versed in comedy. I'd look as much as possible for someone who
doesn't resemble Johnathan Rhys-Davies. Similarly, Tika can be played by any competent, attractive young redhead; Goldmoon is in the same boat. Riverwind, too, is a part that in a lot of ways is perfect for a model-turned-actor type; as long as he and Goldmoon are of an appropriate ethnicity (which need not necessarily be Native American) it works.
It occurs to me that Jack Davenport would make a good Riverwind with a more neutral accent and some good makeup; his stiffness in
Pirates of the Caribbean suits my mental image of the character, minus of course the total Britishness.
Laurana is a bit like Arwen or Galadriel in that any casting will deeply polarise the fanbase. Having the advantage of not finding blondes that attractive, I would simply look for someone young and graceful who can play petulant but believably grow into the Golden General. The "young" part does mean that they're unlikely to already be well-known, though.
Caramon needs someone with good comic timing but also the ability to convey some emotional subtlety; finding that
and the muscles needed for the part could be tricky. You also need someone who can believably grow up severely (and doesn't mind gaining a lot of weight) if there were ever a
Legends sequel. Again, an unknown works better here.
With Kitiara I can afford to be partisan. In the mid-1980s, Jenette Goldstein would have been perfect (and if you don't believe me, check out the classic Elmore painting of Kitiara and Dalamar in front of the Portal). These days, Hell, I might even go crazy and cast Michelle Rodriguez, simply for the sake of contrasting Kitiara's sexiness with Laurana's beauty. Plus she can believably kick ass, and could do well with the right accent coach (you do
not want to have regional American accents running around this film).