http://www.sqlservercentral.com/articles/Indexing/68439/

http://www.sqlservercentral.com/articles/Indexing/68563/

http://www.sqlservercentral.com/articles/Indexing/68636/

http://sqlinthewild.co.za/index.php/category/sql-server/indexes/

Seek - navigation down the b-tree of an index to locate a row or the start or end of a range of rows.

Lookup - single-row seek on the clustered index to fetch the rest of the columns necessary for the query.