Obi website has some recommended routers.if you are a little tech savvy then any router that can be flashed with a third party firmware(DDWRt,Tomato) is a nice router.
in this forum, have not seen people complain about a router flashed with tomato firmware.
i personally use linksys routers and wrt54gl,e2000,e3000 are good ones that work well with Obi