Detect Wifi Hotspots using NetStumbler

NetStumbler (also known as Network Stumbler) is a tool for Windows that allows detection of Wifi hotspots using the 802.11b, 802.11a and 802.11g WLAN  standards. It runs on Microsoft Windows

operating systems from Windows 2000 to Windows XP. A trimmed-down version called MiniStumbler is available for the handheld Windows CE operating system. Its one of the preferred tool for wardriving, which as explained by Jeff Duntemann is

Wardriving is the gathering of statistics about wireless networks in a given area by listening for their publicly available broadcast beacons.

NetStumbler is a small and effective solution for Wifi hotspot detection and completes the network audit toolkit for any expert.
The program is commonly used for:

• Wardriving
• Verifying network configurations
• Finding locations with poor coverage in a WLAN
• Detecting causes of wireless interference
• Detecting unauthorized ("rogue") access points
• Aiming directional antennas for long-haul WLAN links

You can download NetStumbler from here