I have a few Magic: The Gathering cards whose editions I'm having trouble identifying. They are obviously from either Alpha or Beta, since they have black borders and the same design as the Unlimited edition, but how can I distinguish between both editions?
ALPHA cards are black bordered and have very very rounded edges ( 2mm radius ) compared to all other kinds of magic cards ( 1mm radius ). Just pick up a white bordered card and overlay them ontop of each other. If the corners are VERY different then you have ALPHA, otherwise you have BETA.
There are several cards that were corrected between alpha and beta and can be used to instantly identify extremely worn cards. As cited on Wikipedia
This Magic Set Identifier flowchart will help you with any other sets up to about 2001, beyond there it's fairly easy to identify from the set symbol on the card. Thanks to Hackworth for providing an up to date url for it!