I thought I'd share my good experience with a company called "EtherDesigns" at http://www.EtherDesigns.com
They sell custome made cantennas and other 802.11b items (pigtails, omni antennas). I started to build my own cantenna, but his guy has designed a nice model, better than the Super Cantenna.
The FabCorp antenna that Netstumbler and Etherdesigns sell is a great antenna!! I bought one of the cheaper mag-mounts off eBay and was dissappointed in the results. I then bought the FabCorp and found it performed much better, and you don't need a metal surface to use it!
Just wanted to let everyone know!