i know what you're talking about. I use the plastic dvd style cases like these for my wii / ps2 games:
http://www.videogameboxprotectors...
I have put some sealed games in them, but I don't personally think it's a great idea if you're super picky about condition. They seem to move a bit (which could cause surface scratches I'm sure) and it gets a bit clunky putting them in/out of the case where damage could occur. I use them for sealed games that I'm not too worried about (< $50) but I really don't trust them with the higher end games. I usually just get those ones graded or put them in a drawer never to be touched
You could always get the sliding bottom acyclic cases from VGA, but they cost a bit.