Lots of good advice about external mics, and you'll definitely need one if you go down the minidisc route.   Minidisc is great but some will tell you ite obsolete technology. I can't see Sony investing any more money in it. The good news fronm this is that some Minidisc recorders are available at much lower prices than they were a few years ago, and for sound quality it is excellent, especially with a good external Mic.

On the other hand I've has an Edirol R09 for a few years now. The built in mics on these are really quite good. No doubt even better quality can be had from using a good external mic, but it depends how high quality you need the recording to be, I'd recommend doing some recording with the built in mics and then deciding whether the additional expense of an external mic is jusitified.