What's a good router that does dual band 2.4 GHz and 5 GHz and can run OpenWRT?
What classifies a "good" router in your perspective?
However, for supported routers, you can look them up here.
I personally prefer devices with Atheros cards. They have a very active community and the drivers are constantly improving. And nowadays they support 2.4 and 5 GHz.
We are using the Netgear wgt634u for research. It is a very versatile device. But I think today it is rather outdated.
It might not be fast enough (cpu-wise) to fulfill all your needs for a "mini-versatile-server".
If you are looking for a powerful little router, that runs linux (but not OpenWRT), I highly recommend soekris boards. They are more suitable to build a little multi-purpose router. They are highly flexible. And since they are x86 based, it is a bit easier to cross-develop for them.
Hope, this helps.