If you plan to run NeoRouter client on this router, you will need OpenWRT. On Tomato, we only provide NR server, not NR client.
For our internal development, we use Asus WL-500GPv2 (Broadcom) and TP-Link TL-WR1043ND (Atheros). Our current releases support Broadcom routers, and we will add Atheros support in the upcoming releases.
We choose these routers mainly for speed and large flash/ram. They are both very stable and easy to program. TL-WR1043ND supports 802.11n, while WL-500GPv2 does not. Both routers have USB ports.
You can find more options at OpenWrt website http://wiki.openwrt.org/toh/start