CTP3 of SQL Server Code Name "Denali" was made available for download this morning. You can download the 32-bit and 64-bit versions here. Official announcement from the SQL Server team blog and the announcement from the Analysis Services and PowerPivot Team Blog. Note that there was not a publically available CTP2. Microsoft went from CTP1 last November to CTP3.
Aaron Bertrand has some install notes and a Installation Walk-Through. Check out the official Microsoft CTP3 release notes.
The Feature Pack for CTP3 can be download here (note the special version of PowerPivot for CTP3). The new version of PowerPivot is 2.0 and Rob Collie has a post about some new features.
The new Project Juneau features are not on the Denali CTP3 “DVD”/Download, but will be shipped in a separate web release which is coming along very shortly. Keep your eye on http://msdn.microsoft.com/en-us/data/tools.aspx in the next 24-48 hours.
See CTP3 Books Online (read how help is no longer delivered with the software). Project Crescent is also included in CTP3. See the Project Crescent Overview.
Jamie Thomson has a post about the SSIS enhancements in Denali CTP3.
For technical questions about CTP3, go to the MSDN SQL Server (Pre-release) Forums.
Also check out Brent Ozar's CTP3 is Here! Five Things to Know About the Next Version of SQL Server and How to Set Up SQL Server Denali Availability Groups (Brent obviously has been using CTP3 for a while..lucky guy!).