Hi FR
There are some lists of similar characters on the Internet. Nevertheless, I suggest you to make your own list as you go along. Why?
First, because similarity is a gradual, not an absolute concept;
Second, because similarity is a subjective concept, not an objective one;
Thirdly, because two (or more) characters may look almost identical, but one of them may have a very high frequency of use and the other(s) a very low one;
Last but not least, I think it could be more rewarding, if not fun, to make your own list.
Good luck!
P.S.
http://en.wiktionary.org/wiki/Appendix:Easily_confused_Chinese_characters