Rather than make my own unique predictions, I'll rebutt some of the ones made already.
I don't think
Castles & Crusades will be a big thing in any commonly used definition of the word. It'll have some good Internet buzz, which could mean little more than half a dozen really vocal fans are always praising it (about where it is now, actually, at least around here, and I hear about it even less at rpg.net.) It's appeal is too limited; I doubt many people in the market want such an overtly nostalgic experience.
I don't think Eberron will be very impacted negatively by the computer game, should it fail, but it might be impacted positively if the game is a hit. Either way, it appears that Eberron is reasonably successful for WotC, and some hints even indicate that it is moreso than they predicted. But what do I know?
I don't think WHFRP will be a big deal. It's a flash in the pan. Longtime fans will pick it up, and maybe a few new people. Games Workshop are already dissing rpgs in the pages of White Dwarf (according to reports from our British collegues about WD#300 -- I haven't received my copy yet; I'm a subscriber.) I wish all the best to Green Ronin, and I think their strategy of procuring licenses is a good one, but I think d20 Black Company and Thieves World will do better for them.
I think Nisarg's probably right about the new World of Darkness; I imagine a lot of fans of the old World of Darkness will feel a sense of disconnection with the new setting and will drop out. Then again, Campbell's probably right too; I'm marginally interested in picking up the new Werewolf, since I was a big fan of the older one before d20 came out. We'll see if the droppers are a bigger number than the reconverts.
I don't agree with him on Exalted though; at rpg.net there's already a number of threads questioning whether or not Exalted has "jumped the shark." Whether they have or not, I'm sure they're running out of meaningful things to do with the setting. I expect them to announce a Revised edition by the end of the year so they can start the supplement selling all over again.
Rumors are that the dual-stat Delta Green sourcebook will finally come out in '05. That's a lot more likely to be a big deal than anything Amber related. I just can't see that being a big deal one way or another, since the original Amber was so niche. I've never even seen a copy on a shelf at any gamestore ever.
Hmmm... anything else? I guess not. If I think of anything, I can always edit the post...