I don't post too much but you have brought up a topic I can weigh in on. As a computer engineer I have watched the PDA technology develop over the years. I currently have an Ipaq h5550 which is a decent PDA that includes a biometrics fingerprint scanner for secure logon. Slap my little foldout keyboard on it and I'm set for any geek contest.
I want to caution you before you spend $300 - $700 on a PDA. The PDA market has been in a sharp decline for several years now thanks to smartphones. The current standard for cellphones called 3G is impressive. I don't want to get into the weeds on this, but 3G cellphones come with cable modem/DSL bandwidth speeds, embedded GPS functionality and many other advanced features. What manufacturers have done is take these standards and included features of the common PDA into a phone. These phones have become the cancer to the PDA market because most people do not want to carry a phone and PDA when they can combine that functionality into one device. These smartphones can be costly, but nothing worse than a decent PDA.
Of course it's your money and situation that you have to consider, but don't rule out the smartphone when deciding. I think you will be very happy with one.
If you do decide to stick with a PDA you should test the Palm vs Windows operating system to see which you like better.
I do not work for any cellphone provider or manufacturer. I work for the government, so I'm not trying to sell anything. I don't own a smartphone (yet) and really don't know which provider has the best deal.