What is SQL Server "Denali"? What's new?
The new features include : 


Multi-Subnet Failover Clustering  
Programming Enhancements including sequences, ad-hoc query paging and full-text search tweaks  
BI and Web Development Environment Improvements  
Web-based Visualization  
Data Quality Services enhanced 


You can view the detailed review here :  New Features Of Denali  

"Denali" is a code name. Here is the list of the code name of other versions of SQL Server:


1993 – SQL Server 4.21 for Windows NT  
1995 – SQL Server 6.0, codenamed SQL95  
1996 – SQL Server 6.5, codenamed Hydra  
1999 – SQL Server 7.0, codenamed Sphinx  
1999 – SQL Server 7.0 OLAP, codenamed Plato  
2000 – SQL Server 2000 32-bit, codenamed Shiloh (version 8.0)  
2003 – SQL Server 2000 64-bit, codenamed Liberty  
2005 – SQL Server 2005, codenamed Yukon (version 9.0)  
2008 – SQL Server 2008, codenamed Katmai (version 10.0)  
2010 – SQL Server 2008 R2, Codenamed Kilimanjaro (aka KJ)  
2011 – SQL Server 2012, Codenamed Denali