Your best bet is to avoid any media that uses CMC Magnetics dye or is a cheap, unknown brand. One of the main ones marketed with this dye is Memorex. Contrary to what others here have mentioned, not all Taiwanese media is bad, but media made in Japan is always better.
Avoid really cheap media-the disc problems and potential coasters are not worth saving $.10 per disc. Sales reps usually know nothing about media; ask them what media code the product is and all you will get is a blank stare. I suggest downloading a program that can read the media code and do disc tests, such as DVD Info. Check out this link for all the info you'll ever need on the subject.
Others to avoid:
Princo
Matrix
Longten (or any media made in HK)
TDK (inconsistent media codes)
Optodisc
unlabeled/store labeled media, such as OfficeMax brand (almost always CMC)
Khypermedia
Any media made by Supermediastore
Ones to look for:
Verbatim (about the best media money can buy)
Prodisc (Best used with Pioneer burners)
Ritek (good, but slipping)
Taiyo Yuden (Best quality/value for bulk Japanese media)
Maxell (usually Ricoh dye)