Photorealism - then anything that assists you in drawing might be useful.
I would definitely take a look at VectorScribe.
Since you will be drawing freeforms a lot, Dynamic Sketch and InkScribe could be nice as well. As those two make a lot more sense when used with a graphic tablet (WACOM): do you have one?
You might also want to check the books by Bert Monroy (if you don't already have them)
