Well, I guess I'll post by bi weekly tube wrap up.
Good brands=GE, RCA, Westing House, Svetlana, Amperex, Telefunken, Sylvania, Tesla, JJ
If you see anything else, and it's marked JAN, it will be top notch. JAN stands for Joint Army Navy, tough tubes.
Not so good brands=Sovtek, anything made in China, (newer) Fender, Groove Tubes. Fender tubes made from about 95-00 are Sovteks, the ones made for the past year or so are Groove Tubes. Groove Tubes basically takes tubes from various brands and matches them and tests them, then they charge double the price.
Your best bet is to buy from your local amp shop, they usually have a decent supply of tested tubes on hand.
alt.guitar.amps for more info. Pay attention to the posts by Lord Valve. That guy really knows his stuff.