I do use StartSSL but the problem just comes from having multiple sub domains. I get IPv4 addresses for $0.50/mo/each but I'd rather not setup each subdomain on its own dedicated IP for the sakes of using free SSL certs.
Also you could run the distinct (sub)domains on different ports on the same address, though this is perhaps less useful.
Also, with SNI you can use many single-name certificates on one address (and all on the same port) using SNI. Unfortunately there are a number of significant client combinations that won't play nice with this (most notably, if you can't guess, IE on Windows XP): http://en.wikipedia.org/wiki/Server_Name_Indication#Support