AirRadar allows you to scan for open networks and tag them as favourites or filter them out.
This small utility provides you with signal strength, network mode (GRPS/WCDMA/HSDPA), and statistics about your current connection (current throughput, total data transferred, connection time).
coconutWiFi displays you a small aqua-bubble at the top of your screen which indicates whether you're in range of a wireless network or not.
Hotspot Shield creates a virtual private network (VPN) between your laptop or iPhone and our Internet gateway. This impenetrable tunnel prevents snoopers and hackers from viewing your email, instant messages, credit card information or anything else you send over the network.
MacStumbler is a utility to display information about nearby 802.11b and 802.11g wireless access points. It is mainly designed to be a tool to help find access points while traveling, or to diagnose wireless network problems. Additionally, MacStumbler can be used for "wardriving", which involves co-ordinating with a GPS unit while traveling around to help produce a map of all access points in a given area.
This tiny little utility will allow a user to assign AppleScripts to any wireless network, all you need is to know the SSID of the networks and well some resources on scripting with AppleScript.
Wireless Grapher is a widget which tells you the wireless network you are connected to, the channel and also graphs the link/connection quality.