I've used Perforce at multiple companies, but Subversion is a great alternative today. A lot of people's Perforce-vs-Subversion biases were formed years ago, and since then (as a result of pressure from git and all the other alternatives available today) Subversion has added a lot of really great features.

PlasticSCM is a newish alternative. I can't vouch for it, but it looks really good. It tries to give you the best of Perforce and DVCS in one package. It also cleanly solves some problems that are hard to solve in Perforce (e.g. X-links https://www.plasticscm.com/documentation/xlinks/plastic-scm-...).