Open source inSSIDer is a Vista-friendly netStumbler
I had tried NetStumbler before on my Vista laptop and not met with much success. So when I read on MetaGeek's web site that their inSSIDer was designed to do the same job with native Vista APIs, I was intrigued.
If you're a road warrior, this is a great utility to keep at the ready. inSSIDer's scanner makes it a snap to identify available access points, quickly displaying available SSIDs and their channel, signal strength, speed, and encryption type.
Click the edit menu, and you can copy discovered AP data or the chart pane to the clipboard.
It does an admirable job of locating wireless signals, usually picking up at least one that Windows doesn't report. Not that it's very useful, as it's always turned out to be the weakest signal for me. Still, I like to know my surroundings.
inSSIDer is free, open source, and will run on 32 and 64-bit Vista or Windows XP (with the .NET 2.0 runtimes installed).