I've just finished I Have America Surrounded by JMR Higgs, a biography of Timothy Leary. It provides a lot of background on one of Robert Anton Wilson's biggest influences.
Higgs obviously spent a lot of time researching the book, trying to separate fact from fiction (including fiction propagated by Leary himself.) I thought Higgs had just the right attitude, giving Leary credit where it's due for his more interesting ideas and for his optimistic approach to life, but also not hesitating to debunk some of Leary's ideas and alleged achievements. (For example, it turns out that Leary did not achieve an amazing rate of success when he used psychedelics as part of a program to keep criminals from returning to crime.)
The connections between Leary and other famous, influential people were pretty amazing. I knew that Leary sang in the background on John Lennon's "Give Peace a Chance." But I didn't know that Aldous Huxley influenced Leary's approach to drugs, or that Leary was in the helicopter with Mick Jagger at Altamount, or that Leary's cell was next to Charles Manson's, allowing the two to communicate.
If you do read the book, be sure to also read the notes at the end, which contain lots of interesting material.
From Higgs' FAQ at the web site for the book:
I have never read any of Leary's books, where should I start?
I'd start with The Politics of Ecstasy. High Priest is also good if you are interested in the effects of psychedelics. If you like a good adventure story, then try to track down a copy of Confessions of a Hope Fiend, it's out of print but you can usually find it on eBay. I'd also recommend Timothy Leary: Outside Looking In, edited by Robert Forte, which gives a good image of the man by those who knew him.