For the past few years I’ve been using an Apple Time Capsule as my WiFi router. The range was awful but I kept trying to boost it with Airport Express devices. Finally I threw in the towel and bought a new WiFi router, the ASUS RT-N66U. Suddenly we have amazing coverage all over the house, even way down in our basement. I’m kicking myself for not getting this little powerhouse long ago.
[After reading Dan's recommendation, I bought one of these to replace my Airport Extreme, which couldn't penetrate the chicken-wire Faraday cages in my house's walls. This greatly improved the range of our home Wi-Fi signal. - Mark Frauenfelder]