A high density foam paint roller is an excellent tool for painting smooth surfaces. A professional painter recommended using it on the trim in my house, and it really did a great job. These paint rollers produce an extremely smooth finish that is the next-best thing to sprayed-on.
Don't confuse this high-density foam roller with the typical fuzzy paint roller. The fuzzy ones stink -- they leave that characteristic pattern in the finish, and they apply an overly thick coat that wastes paint. A high-density foam paint roller, on the other hand, spreads on a thin coat of paint very smoothly.
Avoid the cheap yellow foam paint rollers. Only the white high-density ones give good results.
Take it from someone who hates to paint -- these high density rollers are the way to go. Quick, easy and quality results. They also clean-up easily and the plastic core is long-lasting (unlike the cardboard core on those awful fuzzy rollers).