My current favorite handheld, the Korean-made Dingoo A320. Emulates almost every console up to, and including, the Playstation 1. Also plays DOS-ported games like Doom, Heretic, etc. Plays MP3s, movies, reade e-books, and has an FM radio tuner.
Gamepark Holdings follow-up handheld to the GP32. Emulates tons of systems, plays movies, MP3s, e-books, etc. A lot of fun but the controller was widely panned. I still love my First Edition, pre-ordered, GP2X.