MVerb is a freeware Reverb unit created by Martin Eastwood. It’s a C++ written plugin so the CPU consumption is low. I tested it a little bit and it sounds very nice – produces similar, “warm” sound as Jeroen Breebart’s Omniverb. It’s worth mentioning that source code is available via GPL license so if you know C++, feel free to improve it even further 🙂 MVerb is also available for Mac users.
Short example (probably too much reverb – my studio monitors fried 😉 First dry example then with MVerb )