The Philips DVP642 does a great job of playing MP3s on DVD-ROM ISO format discs. It doesn't list this ability on Philips website, but I have three of these units and they can in fact play MP3s burned on dvds as data (I use Nero Burning ROM to create them). I haven't tried the DVD-ROM UDF or the DVD-ROM UDF/ISO formats under Nero yet, but I see no reason why those wouldn't work. There are two limitations though: 1) You can't search through your list/menu of MP3s while playing a MP3 file (it has to be in stop mode in order to be able to search through your list of MP3s), 2) The MP3 filenames are limited to eleven characters. Other than these limitations, it's the best DVD player out there for the money.
It can read/play DVD-R, DVD-RW, DVD+R, and DVD+RW discs including MP3s burned to any of those types (I mostly use DVD+RW for my MP3 collections so I can update my discs when I get new MP3s). I have yet to encounter a DVD-Video disc that it won't play no matter which type of disc it's burned to (DVD-R/RW, DVD+R/RW). Additionally, this unit supports NTSC and PAL DVDs. There is also an unofficial "hack" code that allows the unit to become region free (I have personally verified this and it has played all my region 1 and region 2 discs with no problems).
The Philips DVP642 is also progressive scan capable. It has three output types for video: composite, component, and S-video. It's also suppossed to support DivX and MPEG4, but I have never tried any discs in those formats because I don't use them. On Philips website under the product's specs, it only lists the ability to play DVD+R and DVD+RW (not DVD-R and DVD-RW). But, if you download the .pdf file, it lists all discs types (DVD-R/RW and DVD+R/RW). I have verified that it plays every disc type (including discs that KProbe reported very high PI and PIF errors on - due to crappy media brand).
The only other limitation that I have come across is that your are limited to 8X speed for forward/reverse searching. But, that'is hardly a limitation for a unit that is so versatile. Maybe the best thing about the unit is it's price - in the USA it can purchased for $69.99 on average from various retailers. This unit truly kicks ass!