Our Airport base stations were starting to die. Every once in a while, the basestations would still broadcast the SSID, and wireless devices could still connect to them but wouldn't transmit any data to our wired network. Since this was happening to both our Airport Express and Airport Extreme base stations, I assume that there was something, either on the wired network, or some RF interference that was causing them to lock up.
I took this opportunity to upgrade to a 802.11n base station, so I bought the D-Link DAP-2553. This was one of the few dual-band, non-router, base stations. Once I set it up, things have been working a lot better than they were with the Apple base stations.
Setting it up was a pain, though. The manual suggested that all I had to do was connect it to my network, and I would be able to log into the web interface. It also suggested that I could connect it directly to a computer to do the same thing. This wasn't as easy as they claim. By default the base station is configured to have the ip address 192.168.0.50. Since out LAN uses a different subnet, just connecting it to the network doesn't make it accessible to the other computers on the network. Also, connecting it directly to a computer, without doing anything else, doesn't work as the base station doesn't have a DHCP server, so the computer ends up with a self-assigned address.
What worked was to directly connect it to a computer, then I gave the computer a static ip address of 192.168.0.49, with mask of 255.255.255.0. This allowed me to connect to the router, and configured it to get it's address over DHCP. Once I did that, I was able to connect it directly to my network.