I've purchased from Frame Destinations and have been quite pleased with the value for dollar, with the combination of frame, glass and mat the best time saver I've found yet. I've also been ordering from Dick Blick for over 30 years, and will continue to do so, but if I were only buying a few cut mats, it would be from FD rather than the pre-cut cheapies that are in catalogues from places like Dick Blick. You do get what you pay for. Every couple of years I buy a bunch of those that DB sells, and they end up being only usable for quick hangings where the drawings/paintings/photos will be up and down within a couple of weeks.
Of course, if you're willing to cut your own, matboard from DB is fine, but remember what Mahler one mentions: Acid free and archival are not the same thing.