Index rebuild on a large database could take longer time. One of our customer was looking for a solution to rebuild index one by one when index fragmentation is greater than 30%.
Related newsgroup thread: http://social.msdn.microsoft.com/Forums/en-US/sqlkjmanageability/thread/4faae7c8-3e58-4117-8538-f397e342743f
I have written a SQL Powershell script that identifies indexes on tables that have fragmentation greater than 30% and performs a Index Rebuild one by one. You can also control the number of indexes to process in single script run. You can run this SQL powershell script as a recurring scheduled SQL Agent job . More details at: http://sethusrinivasan.wordpress.com/2012/02/14/index-rebuild-on-large-database-sql-agent-powershell-job/