What decks are tournament legal in magic the gathering?

In most tournaments, cards from the following sets are legal:

• Shards of Alara
• Conflux
• Alara Reborn
• Magic 2010
• Zendikar
• Worldwake
• Rise of the Eldrazi (effective April 23, 2010)

This format is called "Constructed."

In Extended format, cards from the following sets are legal:

• Ninth Edition
• Tenth Edition
• Magic 2010
• Mirrodin
• Darksteel
• Fifth Dawn
• Champions of Kamigawa
• Betrayers of Kamigawa
• Saviors of Kamigawa
• Ravnica: City of Guilds
• Guildpact
• Dissension
• Coldsnap
• Time Spiral
• Planar Chaos
• Future Sight
• Lorwyn
• Morningtide
• Shadowmoor
• Eventide
• Shards of Alara
• Conflux
• Alara Reborn
• Zendikar
• Worldwake
• Rise of the Eldrazi (effective April 23, 2010)

There is also a list of Restricted and Banned cards on the Wizards of the Coast website for this format.

In Legacy and Vintage formats, any set is legal, but there are extensive lists of Restricted and Banned cards on the Wizards of the Coast website for these formats.

http://www.wizards.com/Magic/TCG/Resources.aspx?x=judge/resources/banned