The 5 for $5 deal is pretty much an ongoing thing and is great if you plan to visit PI 2 or more times in a 5 day period.
Also, there is a PI annual pass that runs about $60 (inc tax) that gives you 1 year of PI admission. Nice if you plan to be in WDW 2 times during a 365 day period and plan to spend at least 2 nights each trip in PI.
Another little known special is the "Friends Free Fridays" that they have. On Friday nights, PAP holders and PI AP holders can bring in 1 friend for free. Just bring your PAP or PI AP to the ticket booth and ask for your free ticket. The signs say you have to arrive before 9pm but we used to go after work and never had a problem getting the free ticket, even after 10pm. At one time, they even allowed guests who had the regular AP to get in for free (no guest, but still, great if you are an AP holder) on Fridays.