If he'd asked for the cheapest basic router available, I'd agree with the Buffalo WHR-G54s as a decent option in the $40-ish range.
He did not, he asked for the most stable router he could get which the platforms I recommended will provide. He also mentioned that he's got CAT6 cabling run all over his house which is large enough to require localized AP coverage, therefore I assumed that price is not his first concern. While the devices I suggested do happen to include MIMO or Draft-N radios, the feature played no part in my suggesting them since he mentioned wireless is a secondary concern.
http://www.smallnetbuilder.com/component/option,com_wrapper/Itemid,156/
You'll notice that the benchmarks highlighting the performance of the units I suggested put them at the top of the heap in terms of non wireless related functions like LAN-WAN throughput and max simultaneous connections (important for p2p users). Two of the devices at the top of the list are based on the same Ubicom IP3023 network processor (D-Link 4300, Zyxel x-550), while the Linksys WRT54G and other Broadcom 5352 based hardware (Buffalo WHR-G54S) place in the middle or bottom of the pack.
I'm not saying the Buffalo products or other Broadcom reference designed router options are bad, they are simply targeted at the value market and are built with price instead of performance and stability in mind. With the DD-WRT firmware you can certainly extend the feature set of the Buffalo but the limitations of the 2-3 year old basic hardware design and Broadcom network processor can not be overcome. The whole reason the DD-WRT platform has been ported to the X86 platform is to overcome the limits of the Broadcom reference design on which it was originally designed.
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OP: Since we're looking at products that can be picked up at a retail store this weekend, the D-Link DIR-655 at Circuit City for $130 seems like the best bet:
http://www.circuitcity.com/ccd/productDetail.do?oid=165020
Basically the next generation replacement to the 4300 with similar basic features (including upstream QoS, gigabit switch, SPI firewall, etc..) with a faster Unicom network processor and a Draft-N radio for $130.
I could not find a national chain that carries the Buffalo, Zyxel or D-Link 4xxx series routers. Good luck!