I have a two Asus RT-N16 routers, one running DDWRT and other running Tomato USB. I have been extremely happy with them. These guys have monster specs as far as wireless routers go.
Ethernet Ports = WAN x 1 RJ-45 for 10/100/1000 Base T, LAN x 4 RJ-45 for 10/100/1000 Base T
USB ports = USB2.0 x 2
Unit RAM = 128 MB (2x 64MB - Samsung K4N511163QZ-HC25 or 2x 64MB - Samsung K4T51163QG-HCE6)
Unit Flash = 32 MB (MACRONIX MX29GL256EHTI2I-90Q)
Unit CPU = Broadcom4718A, 533 MHz (Factory clocked to 480MHz)
More at: http://dd-wrt.ca/wiki/index.php/Asus_RT-N16
I am ssh'ed into one one of them right now and trying to install webcam drivers into it. I plan to do some fun stuff, including using motion detection etc using the relatively powerful CPU in this router. Could you do anything even remotely like this with Apple Airport Extreme? No.
This is a hacker's router and smokes the competition.
BTW, openwrt is not supported on this router. But as I mentioned earlier, DDWRT and Tomato USB are. And they are both running rock solid for me. Whatever you do, do not use the Asus firmware. It's worse than junk.