New releases (RC3) of the excellent NAnt build tool are now available.
In related news, in case you hadn't seen it yet, version 0.9 of CruiseControl.NET was recently released
I think there may be a misconception out there that CruiseControl.NET is only for continuous integration builds. You can just as easily use it for scheduled nightly builds, and not use the build-on-every-check-in capability. So dip your toe in the automated build water by setting up CCNET for nightly or weekly builds, and then when you're comfortable with that, think about adding continuous builds. Nightly builds can be "full" builds with full tests, and continous builds can be lighter weight builds to speed them up.
Continuous builds can be a huge timesaver by reporting build problems as soon after their introduction as possible. Bad news should travel fast. When a developer checks in broken code that invariably works fine on their machine, but is now incompatible with another portion of the system that they do not routinely build. The build system will send e-mail within minutes to get them to fix it. You don't have to weed through an entire days worth of all of your developers' changes to find out who or what caused the problem. The perpetrator's name is right there in the e-mail alongside the precise files checked in and hopefully a comment saying what they were "trying" to do.