CFEngine is probably the oldest option for automating infrastructure. It is written in C, so it might be a little faster than the other options. It manages server builds, deployment, and management, and it performs some very useful audits and reports. Some really big names are known to use CFEngine, such as AT&T, IBM, Pixar, and Qualcomm.
CFEngine has open-source and enterprise versions. The differences are a little less extreme than with some of the other options, but again, the enterprise version has all the flashy chrome and a few really useful features that make it worth the expenditure for most users who need or want the added benefits they offer.