Mikrotik RouterBOARD 532, they are a bit pricey compared to Linksys, etc. but give you loads more features.

Bascially when you set it up as an AP you can type in how much speed to cap each client to, say 64kbps. This means every client will only be able to receive a maximum data throughput of 64kbps (or what you set), even though their card will still associate at up to 11 or 54Mbps. You can allocate speed as a default option (all clients), or different speeds for individual client MAC addresses, or both.

When buying you will need to purchase the RouterBOARD, an indoor or outdoor case (they are small), a radio card, pigtail lead, antenna and power supply to make a complete unit.

I purchase my gear through www.wisp-router.com, I have found their service excellent.