Look into the Palm TX, MSRP is $299, however, it can be had at a discount or at MSRP with accessories (ie wireless keyboard) included. WiFi is also built in.
I find the Palm OS intitive and easy to use since its inception (mid-late 90's) and is fairly robust. Because the Palm OS is simple, don't be scared off with ONLY 128MB of internal memory. There is an SD slot which can accept and access cards up to 4GB worth of information.
I find it hard to navigate through MS OS windows and yes, I play with them all the time, but just can't get used to it. One window at a time on a tiny display is all I can handle (see).
For the business side of things, there are Palm versions of ePocrates:
http://www.epocrates.com/
and the PDR:
http://www.pdr.net/login/Login.aspx
I've played with my friend's father's (Dr.) and both are easy to use. Check into the sites and you can download some of the software there for FREE. If you don't have a PDA yet, borrow a friend's Palm and try it. I guarantee you will like it. LOL.
When not on call, in the off hours, there's a ton of third party software available and make the Palm TX a multi media machine, photos, eBooks, music (streaming w/ upgrade) and movies / video - Oh yeah, games too.
Get to a WiFi hotspot and you can cruise the Internet.
Can you tell I love my Palm TX and have gotten here via Palm Professional, Handspring Visors?
Good luck.