If you have any Apple equipment, I'd recommend an Airport now that Snow Leopard has Wake on Demand. Other routers might implement it in time (as it is an open spec addition to dns-sd), but for now the Apple ones are the only ones.

I'd also recommend making sure it's dual band if you have any N equipped machines and live in a crowded wireless space. I have all my computers on 5ghz now, and it makes a big difference since it can easily run 2 channels for the full speed. In the 2ghz range, too much interferes with getting decent speeds.

One other thing to consider is if you want to attach storage or a printer to the router and have it shared out over the network.