I use a D-Link G604T.
Wireless ADSL router - works fine with my XBox360 and PC network (both wired and wireless)
Seems OK bit of kit, needs occasional restarts (as all routers/modem I've owned have required!) Only downside is that it makes a bit of 'whistling' noise which is a little annoying (and appears to be a 'feature' of this model) - but as the device is not in earshot it's acceptable.
The D-Link gaming router has been getting excellent reviews, but no idea if it works with the 360. A lot of stuff is branded as Xbox Live compatible, but that doesn't mean it's Xbox360 Live compatible!
If going for wireless you might want to look for an a+g router - as Microsoft recommends these over a standard b+g. click here has a list of compatible routers in their support section