A recent thread (04/04/2007) on this list showed that the ralink chipsets are well supported by OpenBSD. I think any wireless card with a ralink chipset will do the job.
See http://openbsd.org/i386.html#hardware ("Wireless Ethernet Adapters") if you need more information. Maxime Peter wrote: > I'm looking to build on OpenBSD 4.0 (4.1?) a wireless access point for a > small > network. I would like to hear what cards have proven to be the most > effective in this arena. I am very interested in small form factor machines > with possible onboard wireless adapters. The client systems will be running > Ubuntu Linux (Feisty). Thank you very much. > > Pedro