I just picked up a Linksys WRT54G...
http://www.linksys.com/splash/wrt54g_splash.asp
...from CompUSA on sale for $129.
It works great in my house. I have a 15" flat screen iMac hooked up to it using an airport card I just installed downstairs. The router is on second floor with my DSL modem removing lots of cable clutter from my desk! I've also got a PC hard wired into the linksys since it doesn't have a wireless NIC yet. I love it!
If and when I get a powerbook, I look forward to being able to be connected from practically anywhere in the house.
The security features fit my needs. I enabled WEP, disabled SSID broadcasting and setup wireless MAC address filtering so that only my iMac is allowed access to my network. Don't want my neighbors and would-be hackers crashing my wireless party!
I've read that the airport range is not as good as other wireless routers using its built-in nonadjustable antenna, though the $250 model does have an optional port that you could plug a 3rd party antenna into if you needed a boost.
If the airport extreme's USB printer feature supported a wider range of printers, that might have been a factor for me. Since it doesn't support my printer, I decided it wasn't worth the extra $70 for now. Instead I used that money to get an airport card since my iMac didn't come with one.
One other small factor to consider, the Airport's UFO appearence has an appeal to it. It's much nicer to look at than most other wireless routers I've seen. The Linksys I have looks like a black & blue brick compared to the slick looks of an airport.
Hope this helps.