I travel a lot, and like you I enjoy reading on planes and trains. I do have a PDA, but I don't use it for reading e-books, and I have never owned an e-book reader. I've used one though.........once.
In my opinion the reason why these devices are obsolete, or near obsolete, is that there are few things more excrutiatingly tiring than trying to rtead a book on a screen - it's an awful experience, and one which you wouldn't want to repeat in a hurry.
My PDA/handheld recommendation? The HP iPAQ H2210 or the Palm Tungsten T3