A good engineer takes pride in his tools.
As with many things in IT, there are many options to choose from and most work equally well provided the engineer has a thorough understanding of how to use them. I happen to use and prefer the following tools, but your taste may be different. Use what you like and know as long as it gets the job done.
Items with an asterisk are my preferred tools for each category.
Information Gathering:
*AirMagnet Wi-Fi Analyzer Pro
*MetaGeek inSSIDer
Fluke AirCheck
Ekahau HeatMapper (Free)
Xirrus Wi-Fi Inspector
WiFi Scanner (Mac)
Kismet (Linux)
Predictive Site Surveys:
*Cisco Wireless Control System (WCS)
AirMagnet Planner
Ekahau Site Survey
Motorola LANPlanner
Aerohive Wi-Fi Planner (online - Free)
Post-Installation Site Surveys:
*AirMagnet Survey Pro
Ekahau Site Survey
TamoSoft TamoGraph Site Survey
Veriwave WaveDeploy
Protocol & Roaming Analysis:
*WildPackets OmniPeek
*MetaGeek Eye P.A. (protocol visualization)
*Wireshark with CACE AirPcapNx and Wi-Fi Pilot (now Riverbed Cascade Pilot Personal Edition)
Wireshark with Atheros Adapter (Linux)
AirMagnet Wi-Fi Analyzer Pro with multi-adapter kit
AirMagnet VoFi Analyzer
TamoSoft CommView for Wi-Fi
Spectrum Analysis:
*MetaGeek WiSpy DBx with Chanalyzer Pro
*Cisco Spectrum Expert (cardbus)
*Cisco CleanAir Access Points (Cisco infrastructure only)
AirMagnet SpectrumXT
Performance Analysis:
*Ruckus Zap (open-source tool, also built into Ruckus equipment as SpeedFlex)
*ZapPerf (port of Zap tool to iOS devices)
*Iperf (CLI) or Jperf (Java) (both Free)
*2nd Ping Test Tool (Free)
*TCP/IP on Ethernet Performance Model (reference only) (Free)
Veriwave WaveDeploy
Ixia IxChariot
Ixia Qcheck (Free)
Nuts About Nets NetStress (Free)
Security / Pen-Testing:
*Backtrack / Kali Linux
Immunity SILICA-U
TamoSoft CommView packet injection
CACE AirPcapNx traffic replay and injection
Cable Plant Verification:
*PowerDsine PoE Tester
*Fluke MicroScanner Cable Verifier
*Tempo 200EP Tone Probe
*Smartronix SuperLooper Line (loop adapters)
Miscellaneous Tools:
*Nuts About Nets AirHORN
*tftpd32
*Cisco WLC Config Analyzer
*Microsoft Visio