F-4 variations? Can't think of any site. 5053phantoms is THE site for pics though.
http://www.5053phantoms.com/
Here's the F-16 one I was talking about
:
http://www.habu2.net/vipers/viperblocks/index.html Be sure to read Block 40 carefully, that introduced a lot of features. The early F-16C's (block 25) are nigh-identical to the A's, asides from the tail fin (which ended up being purely a cosmetic difference) It was the Block 40 that introduced a lot of little things that now define what most F-16C's are like, after the Block 30 brought in the new engine, and later the new intake.
For anybody who wants, I'll happily type out a quick list of what to look for, if you want to "get started" looking at some pics etc. I can do the F-4, F-8, F-14/15/16/18.
Detailed, illustrated guides take me hours of work, so I'll only do it if there's demand. (With the F-14 such a hot topic lately, I might go ahead and do one for it anyways)