SETI is awesome for underutilized desktop machines / servers. Who doesn't want to help in the search for extraterrestrial transmissions?
I believe the BOiNC project also has other branches, like using your spare cpu cycles for various medical and scientific efforts.
I know the OP was looking for a way to make a quick buck, but giving back is always a nice alternative too.
And to make life easier in getting it installed on your VPS, just run:
bash-3.00# wget http://boincdl.ssl.berkeley.edu/dl/boinc_5.4.11_i686-pc-linux-gnu.sh
bash-3.00# sh boinc_5.4.11_i686-pc-linux-gnu.sh