I would recommend two brands; Cyro GP and Spartech Polycast. These are both cell cast acrylic which is much stronger than extruded acrylic. Extruded acrylic is made in a big machine that rolls out the sheets under pressure, almost like the old playdough toys. Cell cast is poured into a big mold then dried.
Unfortunately, if you buy off brand cell cast you can be even worse off than with extruded, as the off brands usually have very inconsistent molecular weight, which means it melts unevenly, producing poor solvent weld joints. Sometimes these joints can look fine; then under some water pressure they leak. This is a big bummer.
If your fuge is really small, there's nothing really wrong with using quality extruded; Cyro FF is good stuff. Personally I think it's worth it to buy the cell cast, but it is getting pricey. Around here Cyro GP clear goes for around $180/sheet for 3/8" which is the thickness I use for sumps, skimmers, whatever. Last time I could find Spartech, it was $250 for a 5X8 sheet of black; now I can't find it at any sort of reasonable price. For some reason, Cyro black is more expensive, almost the same price for a 4X8 sheet. It's probably a quirk with the local stores; Spartech is considered the premium stuff. The plexiglass that GoldStripe is talking about is PlexiG I believe; also considered good but I've never used it. BTW Goldstripe, tough year for the 'noles.
