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
Apple iBook G3 Clamshell Indigo M6411 AIRPORT 576 MB 366MHz TIGER OSX WORKING
Time Remaining: 18d 21h 29m
Buy It Now for only: £149.95
Apple iBook G3 Clamshell Indigo M6411 2000 WORKING
Time Remaining: 3d 3h 16m
Buy It Now for only: £159.99
Apple iBook G3 Clamshell Indigo Blue
Time Remaining: 6d 21h 36m
Buy It Now for only: £85.00