Linysys (Cisco) WRT54GL (you want the model with the "L" on the end - other similarly named router models are NOT the same, nowhere near the same).

http://www.newegg.com/Product/Product.aspx?Item=N82E16833124190

$52 (they don't show you the price until you put it into your cart).

Excellent router as it comes. Double-excellent if you load third-party firmware on it (DD-WRT, Tomato, etc.)

There's a reason it comes with over 2300 customer reviews and has a five star rating at NewEgg!