Hawking Technology is preparing to sell a new Wi-Fi finder next week that not only can discern wireless networking signals from other 2.4GHz broadcasts (like Bluetooth), but can also tell which directly they're coming from. The HWL 1 has a flip-up communicator look to it, and can display the signal strength with five integrated LEDs. It will retail for around $35, and will come with non-rechargeable lithium batteries (that they claim should work for about 2 years).
It's a little on the big side, at 3.6-inches long, but I could probably live with the size to gain the ability to track down good signals. Now if there were only a way to tell if the hotspot were open without trying to connect with a laptop or PDA.