I've been thinking of getting a Pioneer DVR-105 for some time now. As Masker says, there are a number of reports about the drive at xlr8yourmac.com in the drive compatibility database (search drive type DVD-R DVD recorder, drive brand Pioneer).
So long as you're running the latest version of OS X and iTunes etc, disk burning from the Finder and MP3 burning from iTunes is supported. The only issue seems to be the Kernel Panic upon awaking from sleep, which can be avoided by switching off some of the energy saver preferences.
Apparently a firmware update is available for the drive (different from the 103/104 update) but it requires a PC to do it. I've been waiting until the firmware update finds its way into new drives, and to see whether the next update to OS X fixes the sleep issues.
The best UK prices I've found are <a href="http://komplett.co.uk" target="_blank">here</a> and <a href="http://www.overclockers.co.uk" target="_blank">here</a>.