For PS Plus I was wondering what free games are instantly available when you subscribe? This link says about 18 are available but it doesn't say which ones. Also, when you sign up, do you have access to past free games like Spec Ops or do you have to purchase it at the PS Plus price?
here is the current list
no, you don't have access to past free games unless they are on the list in the link above
The Store will always be up-to-date, and is now the best way to browse the current IGC through a web browser:
From anywhere within the Store, click:
Games --> PlayStation Plus --> Free Games