Let's face it... the iPhone's built-in Wi-Fi finder is inadequate, listing only a few of the strongest networks in range. That's where WiFinder comes in. This free utility is excellent at detecting as many Wi-Fi hotspots can be found.
There are a few things that don't work quite right, though, and these make WiFinder difficult to recommend. The first thing is that the automatic rescan feature doesn't always clear out hot spots from the list as you move away from them. The second thing is that when connecting to an open hotspot, the utility will say "connected" even if it never succeeds in actually connecting to it. The last thing is that WiFinder is unable to connect to security-based hotspots, even if you know the key.
There are several other Wi-Fi finders in the App Store. It's likely that one of the other apps, perhaps a paid app, won't have all these little issues plaguing it.