http://forums.studentdoctor.net/forumdisplay.php?f=109
Is a good start, but we have no FAQ for that section. Something we should think about.
Briefly: there are two major PDA systems - Palm and Windows. There are many manufacturers for Windows based PDAs, but only one for Palm. There are combo phone/PDAs, but that's another discussion entirely.
There are advantages/disadvantages in choosing either. Palm has been around longer so there are more programs for the Palm PDAs, but the major medical apps - Epocrates and the Skyscape collections are available in both Palm and Windows.
Regardless of which you buy, you definitely want expandable, removeable memory capability. So you can store that massive Stedman's dictionary or derm book.
Other than that - wifi, built-in keyboards, cellular capability - that's up you.
We should really work on a PDA faq. Hmmm....