The Tomato firmware for routers seems to be good software. It's a simple replacement firmware for the Linksys WRT54GL and a few other Broadcom based routers. It's tightly focussed on being a good router, nothing more. And it has decent documentation.
The main feature it has over most routers is Quality of Service routing. The default configuration once you turn it on gives priority to DNS requests, small Web requests, and outbound ACKs. That last feature is really important; it should solve problem that a single upload totally kills all downloads on an asynchronous connection like residential DSL. I also tweaked it to give ssh and ntp priority.
The other main Tomato feature is fancy bandwidth graphing. Overkill for me, but cool. And the firmware has lots of knobs to turn; I like being able to tweak the NAT connection tracking.
Tomato isn't going to solve my problem of flaky router hardware, but at least the software may work sensibly. The QoS feature should be a significant improvement. Hopefully some day a consumer router manufacturer will get smart and build QoS in to their products.