I usually recommend the ASUS RT-N12vB1 because it is good value for the money. It does 802.11n 2x2 for 300 mbps in the 2.4 GHz band. Dual 5 dBi antennas for excellent range, 8 MB of flash for good firmware support and decent future expansion, and a 300 MHz CPU which should be good for around 45 Mbps of routing under typical circumstances. Install Shibby's Tomato firmware for maximum reliability.
»tomato.groov.pl/download/K26RT-N ··· -Max.trx
If you want dual band wifi (2.4 + 5 GHz) go for the RT-N66U with Shibby's Tomato (use the right build for the hardware). If you don't care about dual band and just want a faster CPU or 3x3 wifi, go for the RT-N16.--