Rake.NET

Offers several Rake tasks that make building .NET projects easier.

Convention over configuration (we don't make you tell us where msbuild.exe is, we use the registry and we let you override the path)
Rakefiles should be specification files and free of 'implementation' details

MSBuild - for compilation, but any target is supported
Install coordinator
- Generates/updates a Paraffin WXS fragment
- Running a WIX build using MSBuild
- Embeds the MSI in a dotNetInstaller based bootstrapper for .NET framework prereq, etc.
- Uses signtool.exe to sign both the MSI and EXE with a code signing certificate
NUnit - NUnit console runner for running unit tests
BCP - seeding SQL Server databases with comma separated value files (and handling escaping properly)
Google JS Test Driver
SQLCMD - executing DDL against SQL Server databases
Yahoo Minify JS support (using Java library)

Price: Free