KisMAC

This popular wireless stumbler for Mac OS X offers many of the features of its namesake Kismet, though the codebase is entirely different. Unlike console-based Kismet, KisMAC offers a pretty GUI and was around before Kismet was ported to OS X. It also offers mapping, Pcap-format import and logging, and even some decryption and deauthentication attacks.

inSSIDer

inSSIDer is a wireless network scanner for Windows, OS X, and Android. It was designed to overcome limitations of NetStumbler, namely not working well on 64-bit Windows and Windows Vista. inSSIDer can find open wireless access points, track signal strength over time, and save logs with GPS records.

P0f

P0f is able to identify the operating system of a target host simply by examining captured packets even when the device in question is behind an overzealous packet firewall. P0f does not generate ANY additional network traffic, direct or indirect. No name lookups, no mysterious probes, no ARIN queries, nothing. In the hands of advanced users, P0f can detect firewall presence, NAT use, existence of load balancers, and more!