The best drives come from NEC. They are very good burners and decent readers with excellent modified firmware support (thanx to people HERE ) And they are very affordable too! ND-6650 around 80 Euros.
As for DVD-ROM drives, I don't know too much, try to look around on this site. You might find good ones on eBay, used but vey cheap.
Definetly avoid LG and Samsung!!! (Well, LG does have a decent burner released now, it is built in the Fujitsu-Siemens Amilo series and it works very good, but it costs more than NEC)
You must decide, but consider that a DVD-ROM drive can have more problems with with reading than burners. And do not buy combo drives, they are almoust expensive as DVD writers!