I found Olympus digital recorders shortly after starting law school and I was pleasantly surprised. I had a more entry level recorder, the DW-90, and I'm not even sure that they make it anymore. Plugging it into my laptop's USB port with a cable that came with the recorder, I could record for as long as my hard drive could store it and at high quality. Until a few years ago, their website was less than helpful as far as support for these recorders (offering games(?) rather than drivers for these recorders). Not sure if their human customer service has changed for the better (their website has) but overall, Olympus digital recorders are awesome. For a classroom setting (not sure about lecture halls, though) the DW-90 worked well all through the room and playback was great. I believe the DW-90 was sub-$100 so you don't need to spend a small fortune for good quality.
I don't know about these dedicated recorders, but i do know one thing. Many mp3 players that have a mic are good enough for the class lecture or seminar. My SanDisk 256 mb player can record 17hrs on 250 mb. This is only wav 8khz after all, but i find it more than satisfactory.
Hi - I hope this is useful we put together a dynamic matrix that allows you to compare several popular digital voice recorders (including all in one units) side by side. It is kind of a fun tool, you can remove features, only view features that differ etc.
Also check out the Photo galleries, sort of my fav site feature because it allows you to see a close up of the recorder. hope this is helps, and please feel free to email me ways we can enhance the web site, matrix, gallery.
Recorders.com (forgot to mention we have give aways on our forum, this month it is the Olympus WS300)