Below is my old post of upgrading SQL Server, there is a new check list published on codeplex.com SQL Check List which includes more information.
This is is a check list I used a while ago after upgrading SQL Server 2005 to 2008:
1. Update compability level:
alter database [database] set compatibility_level = 100
2. check data purity
dbcc checkdb [database] with data_purity
3. Update page verification
alter database [database] set page_verify checksum with no_wait
4. Update usage
dbcc updateusage [database]
5. Update statistics
sp_msforeachtable ‘update statistics on ? with fullscan;’
Note: Step 5 is recommended to done manually on large tables for accurate statistics periodically.