First of all, use the search facility to search this topic for 'palm software', it has been discussed before and some useful stuff was tossed around.
Second, although not the latest and greatest, I have a few programs that have established permanent residence in my m100:
"CoPilot" by laurie davis. Excellent flight planner, got it free from Handango. Useful from a C172 to jets, dead useful for diversions, etc, where is such and such a waypoint, etc. Combine it with the excellent waypoint generator
http://navaid.com/CoPilot and you have a powerful pre and in flight planning tool
"YAUC" ('yet another unit converter') small unit converter that converts just about every known SI unit to imperial (and Roman) units. Want to explain how powerful the new Ford 260kWatt V8 is to a Yank ... YAUC.
"FlyBy E6B" is an excellent whizz-wheel replacement, cost about US$15, I was happy to pay for it after the trial. Download trial version for free
Likewise, "eSixB+" is a good whizz wheel replacement, with the ONLY daylight/darkness calculator i have seen that allows you to choose 'evening civil twilight' as against sunset.
If you don't have Documents to Go, get yourself a mini-Excel spreadsheet. TinySheet is good. I use it for other calculations including one inop PNR/LPSD/ETP and similar.
AvantGo will allow you to download the flight schedules of local airlines so if someone asks 'will the pax in 8D be able to catch another flight to SYD if he misses his connection..." you can see if there is another scheduled flight. Etc
Palm. Dont leave home without it!!