I finally upgraded my internal network to a Linksys (Cisco) WRTG54GL. Why so specific? I had been reading about the open source project DD-WRT for a long while now and finally hopped on the bandwagon. You need to make sure your router is supported before jumping in and flashing it.
The article that tipped the scale for me was over on HackAttack and since my allowance was still burning a hole in my pocket I shot over to NewEgg and got the router. Upgrading was as simple as the article said, flash it with the mini version, then the full version, and start configuring.
There are too many features to itemize here. Simple put, my little router went from "oh that's nice" to "thank god that's one less thing I have to chase down later". Geek nirvana in many ways. It was a fun little project. Aside from changing the wireless security, it was plug-n-play for my network.
A very nice upgrade if your in the market.