You could try having a base unique-ish password preceded by a site/service specific unique prefix... so a unique-ish base you would remember "pa$$word" on google would be $go-pa$$word on facebook would be $fb-pa$$word and so on.

I guess if someone a) cracked the password and then b) realized you were using some sort of prefix pattern for all sites they could somehow exploit that, but it's definitely better than the same 4 passwords for everything