Virtualization - OpenVZ and also SolusVM, VDSManager
Control Panels - DirectAdmin, ISPManager (all products ispsystem), cPanel
Billing systems - Ubersmith Pro/DE (great experience), WHMCS, BillManager, ClientExec
Of course this is not an exhaustive list of what I encountered, you can specify in PM.
First and foremost, I would like to work for a company that is engaged in VPS or dedicated servers (btw, companies with Ubersmith and WHMCS would be adorable for me, because I love these programs, they are very comfortable). This may be work as asystem administrator and work as a support representative who cares about issues in timely manner.
And I live in Russia (UTC+5) and do speak both English and Russian, it allows me to easily handle the night shift (US), this is especially beneficial for those who want to have a billing & sales support at night.
I will be glad to answer any questions, waiting for them in PM.