No matter what recorder you choose, your equipment is only as good as the microphone you connect to it. The best kind of microphone depends on the situation in which you are recording - there is no universal mic for all settings. That said, you would probably do better with a directional mic (not an omnidirectional one!), as it will help to eliminate environmental sounds, like wind or crowd noise. They also tend to be hardier than other kinds of microphones. It should be noted that recording good dialect samples requires more than just shoving a microphone in someone's face. Gillian Lane-Plescia uses a "lapel" mic, and instead of clipping it on someone's jacket, just places it on the table in front of them. Lapel mics can be great, but they also pick up body noise, like scratching of whiskers and the rustle of clothing.
You will also need headphones. I recommend the cheaper, lightweight kind that come with most portable tape players, as they allow you to hear both the recording and what is going on around you. However, if you want to hear the real quality of your digital recording, you will need the kind of headphones that fully cover your ears, often called "studio" headphones, to block out the sound around you.
Gillian's experience also suggests the use of rechargeable batteries:
"On my recent trip to Ireland, I took my MiniDisc recorder, with a Sony tie-pin mike, and my little Sony monaural TCM 59V, which has an excellent built in mike. The only problem with the MD recorder is that it uses enormous amounts of battery power, and romps through batteries at a great rate, sometimes dying in the middle of a taping, which can slip one's notice if one is not watching the display. I use the wall plug when I can, but it's not always feasible. The quality of the recordings is excellent. Even if I just set the little [lapel] mike on the table in front of the speaker, it still picks up very well. It is quite a delicate instrument so has to be handled carefully"
Her use of a "backup" analog recorder is an important idea: even if the quality is not quite as good, having any recording is better than none at all. If something happens to your recorder in mid session, you have the audio cassette to help fill in the blanks. She also mentioned that the built-in microphone of her inexpensive and more robust analog unit makes it convenient for quickly whipping out when she meets someone she would like to record. Setting up a microphone and checking levels with headphones, as one must with a sophisticated digital recorder, can be a real chore and can put off your sample donor. "I have made some excellent recordings with it in my pocket; recordings of conversations that would have ground to a halt if the Tape Recorder had been produced!"