The memory sticks are only 3.1mm thick and they are available in 1GB, 2GB and 4GB capacities. The stick weighs only 2g and is only 42.6mm long and 16mm wide. Transcend says they have a max read speed of 9-10MB/s and a write speed of 2MB/s.
The 1GB stick costs $15.90, 2GB goes for $25.10 and the 4GB one will cost you $48.30.