Isolation Levels in SQL server 2008 onwards

There are 5 isolation levels supported in SQL server 2008:-

1. Read Uncommitted
2. Read Committed 
3. Repeatable Read
4. Serializable
5. Snapshot  

Isolation levels protect data during sql server transaction against dirty reads.

Found an excellent and simple post on this:- 

http://gavindraper.com/2012/02/18/sql-server-isolation-levels-by-example/