Seti@home & BOINC.
Have previously run Genome@home. Tested UD (Think) folding@home & distributed-folding.
Stopped running genome mainly since this was transformed to use the folding@home-client, and got fed up by teams constantly looking for new project then some difficulties arises.
UD atleast before was crappy client. All of these clients needs much more baby-sitting than seti@home, either due to no good caching or time-limits. Of course, if they're ported to BOINC it's much more interesting to crunch any of these.
Since both folding@home & distributed-folding have the ability to set the priority, both these can run together with other projects, and together with seti@home.