I've used Palm handhelds for a few years now. My first was a Palm professional 3 with a whoppng great 2MB of memory, and after it bit-the-dust my current employer bought me an 8MB Palm m105. Following are some links and resources related to Palm's and my experience with them.
The Palm pilots ship with *most* of the applications you'll need for general use. However, there are so many freeware and shareware applications and games out there, and its so easy to install them, that you'll end up spending loads of time evaluating, installing and using all manner of things.
Whenever I'm looking for something new I generally start with a browse of one of the following sites:
The following tools I use pretty much on a daily basis, and those that arent freeware are useful enough to be well worth paying for. They're not installed by default but are definately worth the download/install effort. email me for an unbiased opinion on their capabilities, use, value or performance etc.
Most of the commercial app development for the PalmOS is done using Metroworks CodeWarrior which is an IDE and compiler for C++. The only problem is that unless you qualify for an educational/academic discount, the product can seem a little pricy. For a cheaper C++ alternative with a Visual studio like interface have a look at MobileStudio and PocketC.
If you're not a C/C++ boffin and are keen to have a crack at developing your own Palm apps, check out Michael Winikoff's Alternatives to C index. One I'm intersted in is a Python interpreter called Pippy, there's an article on IBMs developer works site about it.
Palm themselves have loads of useful online developer documentation. There's a useful looking cookbook-like list of recipies. There's also a list of file-formats and data structures.
You should also have a look at pda-archives.com excellent index of Palm development software for different platforms/languages and the Palm OS Programmer's FAQ.
If you're interested in developing apps for the Palm OS, you'll want to download the emulator from Palm themselves. The only problem being that you have to regsiter with their developer programme to get the ROM images for each device you want to emulated.
Of course, you could always copy the emulator from one of the naughty folks like Mr Taxi who have been through this process on your behalf.
Other things to check out, the Palm OS Emulator HOWTO