$400? You'd be hard pressed to find one that comes even near that price for basic home users
If you're not restrained by a budget, macs work best with an airport extreme or express. But then again, macs work well with all sorts of routers. Many routers have lan ports for wired connections as well as wireless ones. You'll only need a wireless g router; macs only have g cards, but I've heard that the new imacs may be wireless n capable.
It depends on what you need - I don't have any wired connections, so I prefer the airport express because it has wireless printing capabilities. My old D-Link was great, and was configurable via a web browser with many options.