Heart Rate Monitor – I personally like the one’s from Polar, and would go for the most basic model – IMHO anything but the current heartrate is not particularly useful
iPad/iPhone/iTouch – any of the above will be a great companion for your training regime, be it for measuring and timing, for your exercise journal, or simply for having the necessary information at your fingertips
MyNetDiary – for logging your calories and exercises, making sure you stay in the Zone
GoodReader – So that you can take all your articles and videos from the CrossFit Journal with you to the gym
Boxing Timer – To run your favorite Tabata (or any other kind of) interval training
PlainText – Ideal to keep your exercise journal in synch on all your computers and on the cloud (uses Dropbox)
Spotify – For your workout soundtrack
Nike+ GPS – Particularly good in the iPhone where it uses the GPS to track distance (and itinerary) whilst running. Also works on the iTouch where it uses the motion sensor to count steps.