Geoffrey Rush's impersonation of Peter Sellers in The Life and Death of Peter Sellers is excellent. His Dr. Strangelove in particular is flawless.
Look out also for a very hot Charlize Theron.
The film portrays Sellers as more child than adult through his life, but doesn't really go any deeper than that. So if you prefer your biographies to provide some kind of psychoanalytical explanation -- troubled childhood etc -- then this one will leave you dissatisfied.
In all, a clever film about a lost, lonely man.