I'll concur with the WRT54G. Make sure you get one of the earlier versions though, as the Linksys changed to VxWorks with series 5. So you'll want to get one with an earlier revision. They made this switch in order to cut their manufacturing costs, as the VxWorks embedded system allowed Linksys to halve their flashram and ram requirements.

Luckily, Linksys now produces the WRT54GL (due to high demand), which is exactly like the old systems so it can run Linux! So like HTRegz mentioned, you can run the Sveasoft firmware, or even better, the OpenWRT linux distribution. This lets you do a ton of cool things, like Kismet drones, traffic shaping, Radius authentication, VOIP QoS, etc; all the things the big boy routers do. And you can boost the transmitting power, so you can boost it past it's range of 980 feet, so it should be sufficient.

If you're interested in OpenWRT, they have quite a hardware compatibility list.

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