The range of solutions is very diverse and most often very proprietary. Some products operate more as a controller with very thin dumb Access Points and not like a "traditional" network switch at all, others enable more capability with their own smart APs and make a "best effort" when APs from another manufacturer are being deployed. Most are switches are designed to be isolated Layer-2 subnets, others are capable of exploiting routing opportunities at Layer-3, the network layer of the OSI model.
As a prelude to the list of companies, it is important that one understand that many of these organizations are engineering companies with interesting technology, masquerading as product companies. Most won't be around in 24 months either because they blow up or they are acquired. But you asked so here is my list:
Airespace, Airflow Networks, Aruba Wireless Networks, Bandspeed, Bluesocket, Chantry Networks, Cisco, Extreme Networks, Foundry Networks, Legra Systems, Meru Networks, Nortel Networks, Symbol, Trapeze Networks, Vernier Networks, Reefedge and 3Com
This was first published in January 2004