Hi Sally.
I used an Olympus LS-10 linear PCM recorder for my research because that was what was available to me through my department.
If I were buying one for myself for my fieldwork now, I'd probably get one of the Zoom recorders - they're easy to use and have really good sound quality. The Q3 also has an HD camera as well as being a really high quality recording device just for audio if you want. But if you don't want video, then all of the Zooms are really good sound quality, really durable and designed for fieldwork type activities. (source: my husband works with qualitative research and music. He uses a Zoom)
It's worth doing a bit of research and working out what functions you really want. There are also lots of comparable cheaper ones on the market now too.
Hope that helps. Let me know if you have any more questions.