I second the WorldWorks suggestion. The WotC Dungeon Tiles aren't bad, either. I have a number of SKG sets as well, but I wouldn't really recommend them. They're a little too cartoony for my tastes, but I know a lot of folks that like them, so YMMV. I've also used Dundjinni to create my own tiles. That works really well.
Instead of cardboard, you might look at foamcore or mattboard to glue them to. You can find both relatively cheaply at hobby shops, and Target, Walmart and the Dollar Store occasionally run specials on foamcore for a buck a sheet. Mattboard is more of the same width as the WotC tiles. (I huge sheet of it, just haven't glued the tiles yet.)
Speaking of glue, I'd recommend sprayglue - it will save your tiles from warping. Most normal glues have relatively high water content, which can cause warping - and warping not only looks bad, even worse it can affect how minis rest on the tiles.