I think the other posters summed it up nicely... If you insist on mining with your CPU, altcoins are your only option.
I'd personally go for ETH or Magicoin, but you'd need to study the market beforehand.
An other option is to use your server for other stuff... For example, install OpenVZ on it, and rent out VPS's. I think you'll make a lot more money splitting your server up in 20-30 VPS's and rent them out for 0.005-0.01BTC a month than you'll make mining altcoins (offcourse, mining altcoins can bring you a lot of profit, but in this case it depends on luck instead of calculations)
VPS mining is hard to make money off of. I don't believe the math of it being profitable unless you show more details. It's just VPS mining did not last long on profitability. Also VPS that are cheap a lot of time don't allow mining, they have in TOS about excessive usage. And mining run's CPU's hard so a lot of bargin VPS's you get kicked off for mining.
Have you done this? Can you point to a VPS that math works out to a profit? I just don't see it.