Open-wrt Suggested Small Devices

  1. wr703n: modified to 16M flash + 64M ram. Power: 5V*100mA = 0.5W (80mA w/o wifi).

  2. GL-MT300A: 16M flash + 128M DDR1. Power: 3W.

  3. Big for home: MTK7620A ; 2nd hand Mercury.

Alternative With Battery

TL-MR11U 2000mAh, replacable battery.150Mbps ¥ 139
TL-MR10U 2600mAh, bulid-in battery. 150Mbps ¥ 160

Abbreviations

POE: Power Over Ethernet.
SMA: antenna port.
TTL: serial port. (Transistor Transistor Logic circles)

Not Suggested

720n: maybe CN-specific hardware. (Though with double power inputs ; wan+lan ports)
702n: no-USB out port.

DD-wrt

Please see Openwrt instead ;)