Adobe Photoshop 6.0 is the main program in use on this site... its probably the best program out there in my opinion. you can probably download a trial version somewhere like www.download.com and then go find a patch for it that will make it the full version... but you didnt hear that from me...
You can't patch an adobe trial. You will need to download the entire program (100MB-ish). You could do that on kazza or something like that. You might want to look into 3dMax, Bryce, and some other 3d progs.
I use alot of programs both bought and free. There's Photo Shop & ImageReady 6.0 , PhotoImpact 4.0 (which came free with a scanner), Photo Express (which came free with another scanner), AutoCad & SurvCadd 2000, Photo Studio (it came free with my digital camera), Microsoft Photo Editor (comes with FrontPage so it's not free, just a bonus) and never forget about MS Paint which come on Windows. They all do a little something different and when you blend them together you get original and unique results.