Adobe Photoshop with the stock filters. PSP is getting really good as well, if you want to spend less.
A popuplar misconception is that you have to use a 3D app to make something look photo-realistically 3D. The power of a 3D app is making a model and then not having to re-make it when you want a different perspective on the object in question. I know some people really, really like 3D apps, but people have been rendering images with realistic depth for a thousand years with no help from 3D studio Max
I have been accused several times (quite vehemently) of using a 3D program to get realistic results, and I take it as a compliment. With stock and hand-done drop shadows,a good grounding in perspective, and an understanding of negative space you can make any image that someone with 3D Studio Max can make.
I had a guy argue with me for an hour once on IRC that I used a 3d app on Necropolis of Memory: http://www.artuproar.com/zoom.php?num=6185 I guess it has a stock-3D kinda look with the wire and whatnot.
Granted, if you are gonna animate you work, or show it from various angles, etc., you're in for exponentially more work. SO if you you are gonna do photorealistic animation, or make a photorealistic character that you will be reusing over and over, maybe a 3D app would be worth it. If, though, you are gonna just make 3D abstracts and the average fare one sees on 3D wallpapers, you could do the same with a good 2D graphics proggy and build a lot of artistic skill at the same time; and those skills you could use in *any* other medium.
