http://www.adobe.com/products/photoshop/family/ is a good place to start if you're curious of the latest.
Personally, I have Photoshop CS, and it works more then well for me. I've also used 7 in the past, which is also rock solid. I had an opportunity to obtain CS, and I did, 7 is still more then enough to do anything you see here, and you'll still get a lot of support for it from sites and whatnot. If you've never used a program as deep and powerful as photoshop before, 7 will blow your mind.
I haven't had a chance to try out the new CS3/4 since they really redesigned the program, but I hear good things of course.