Karsten Berns of the FZI Research Institute for Information Technologies maintains an online database of historical and current walking machines called the Walking Machine Catalog. Entries range from the earliest steam-powered mechanical man in 1893 to more recent bipeds such as Honda's Humanoid Robot. Walkers are indexed by number of legs, by country of development, and alphabetically by name. You'll also find entries on exoskeletons and other exotic forms of walkers such as underwater walkers and wall-climbers with suction cups.