[pushrax]

StartSSL is free and simple to use unless they changed recently. The only downside is that certain UAs don't trust the StartSSL CA, notably Java.

[donniezazen]

The free version doesn't come with wild card. So if you run multiple stuff off your VPS you will have to upgrade. I currently use self-signed certificate for everything except when I serve content to public I switch to http.

[pushrax]

You could use SNI and support the majority of clients.