There are many VPS services for Linux. Amazon EC2, for example should let you use pretty much any Linux system image you want and they have many available for

There are many VPS services for Linux. Amazon EC2, for example should let you use pretty much any Linux system image you want and they have many available for easy installation. There are also some VPS services for OSX, which should be easy to find with a Google search. I'm not sure if there are any single services that support both Linux and OSX.