I have recently been trying out the Philips Voice Tracer 7880 mp3 recorder and am very impressed with it.
It could be an alternative to the iRiver recorders that were so popular with podcasters before, but now do not feature line ins or work well with Macs.
It has a built-in mic and speaker (good enough for playback in class) and 2 different sensitities of microphone. You can also select super-high quality, high quality, or 3 other lower audio qualities.
It records directly to mp3 and functions as a flash drive without any need to install any additional software (although it does come with this software if you want it). It also works just as well on a Mac as it does on a PC, and has a line in.
What more can you ask for?