If your are considering buying an iBook Clamshell, I would try to get hold of one of the Graphite or Lime G3/466 SE (Special Edition Clamshells) first. These models have the highest spec of the range (466 MHz processors) and are the only models that have DVD-ROM drives, if you don't need to play dvds then the indigo model is a good choice.
All the later models can be officially fitted with a maximum of 320MB of RAM, though it has been reported that they can unofficially support 512MB of RAM, Clamshell memory can be purchased from Crucial.
Apple Clamshell iBooks for sale on eBay
Ibook G3 Clamshell Firewire Graphite
Time Remaining: 2d 8h 21m
Apple iBook G3 Indigo Clamshell M6411 OS904 64MB RAM bundle
Time Remaining: 26d 7h
Buy It Now for only: £124.99
Apple clamshell iBook with issues
Time Remaining: 5d 15h 26m
Apple iBook G3 Clamshell Tangerine 300mhz with 192 MB Memory
Time Remaining: 13h 6m
Buy It Now for only: £125.00