Ask HN: Got new hardware. Want to run vm's. What shim should I use?

Hi All,

I just got some brand spanking new HP hardware. Was wondering what the community would suggest I use if I want to run linux virtual machines. Which hypervisor/shim whatever should I use? I may pay Citrix or VMware in the future but am looking for something to run now on this machine for development purposes.

Links and war stories please. Thank you!