Based on my wholly unscientific testing, and opinion, here is my pick for the top 10 free Windows Mobile tools for the security professional:

1. Cain - a subset of the handy functionality available in Cain & Abel, including cracking support for LM, NTLM, MD2, MD4, MD5, SHA1, RIPEMD160, CiscoPIX and MySQL hashes, decoders for Base64, Cisco Type 7 passwords, Cisco VPN Client passwords, and VNC passwords, and support for dumping ActiveSync, Pocket IE, Pocket Outlook and Pocket MSN passwords from the device. Very handy set of tools, although the practicality of cracking hashes on a Pocket PC is dubious.
   
2. btCrawler - a simple and easy to use Bluetooth scanner, bluejacking and bluesnarfing tool for devices with Microsoft Bluetooth stacks. Note that most of the exploit functionality is disabled by default until you add some custom registry entries.
   
3. vxUtil Personal - a suite of network utilities , including DNS lookups, finger, IP subnet calculator, ping and ping sweep, a port scanner, and more.
   
4. WiFiFoFum - a wardriving and wireless scanning tool. Supports all wireless cards, wired and Bluetooth GPS units, and multiple export formats including text, Wi-scan, Tom Tom POI, MemoryMap and Netstumbler (ns1) formats.
   
5. Spybot - Search & Destroy - the Pocket PC version of the popular Windows spyware scanner.
   
6. Netcat for CE - the "network swiss army knife", for Pocket PC. Not everything works quite as it does on Windows or Linux, but the main functionality is there.
   
7. NBTStat CE - find those NetBIOS shares quickly using the Pocket PC version of NBTStat.
   
8. VNC Viewer - complete the trio of GUI clients by downloading this handy little VNC viewer. Supports both VNC 3.x and 4.x servers, full screen mode, and screen rotation.
   
9. OpenVPN - VPN into your home network (or other networks running OpenVPN) from your Pocket PC.
   
10. Citrix ICA client - Supporting most of the same functionality as the Windows client, this allows you to login to those Citrix machines you need to access.

Honourable mentions also need to go to:

• PocketConsole which allows you to unlock the power of the console, since Microsoft doesn't ship a console application with Windows Mobile. This also allows you to run text applications ported to PocketPC such as Pocket GnuPG and SNMPUtils. Unfortunately for me, it doesn't seem to work on my phone.
• Pocket PuTTY - Pocket PC port of the PuTTY ssh and telnet client.
• Skype - not a security tool per se, but since a lot of security professionals use Skype, its a must have on the Pocket PC.
• ppcPodcast - not strictly security, but allows you to download those security podcasts directly to your phone.