I have an S5 with two flash cards 80 and 128M each, I have lots of A/C parts databases, avionic tooling databases, connectors/tooling spreadsheets. Compass swing and other test spreadsheets, a flying utility which works out all sorts of useful things (even though i don't actually fly). I also have an Acrobat reader on it which enables me to have almost the entire B737-3/4/500 maintenance manual which makes for a handy quick reference. With the acrobat reader you can have just about anything on it, especially if like me you have an acrobat creator. You can even save a whole website in pdf to view it at your leisure.
E-mail and internet of course, which is very easy to set up, you can even get a little program for writing your sms messages on your Psion then point it at your infra red mobile phone (mines a Nokia 6210) and away they go.
I've had Psions for years and I'd be lost without them, I keep about 5 backups located on two different computers and a CD just in case as I'd be lost without it.
Let me know if you need anything else.