I came across this Reddit discussion today. It covers a number of topics, including a current Amex Offer available for $10 off $15 spent on Hulu. But the more interesting revelation for me (maybe not for you?!) was that there are eBay sellers of HIGHLY discounted annual (or 6-month) Hulu subscriptions.
I was able to buy a 12-month Hulu gift card on eBay today for just over $20 (just search for "Hulu gift card" at eBay). What you are actually buying is a $100 gift card. When you go to apply it to your Hulu account (either a new or existing account), you have the option of getting 12+ months of service for that $100 ($8/month) or 8+ months of their "commercial free" service ($12/month). Whichever way you go, you're effectively prepaying your Hulu service for 80% off face value. (Which is better than the 67% off you'd get using the the Amex Offer.)
Warning: As some people note on Reddit, there's some risk that the people selling these codes on Hulu are buying them with stolen credit cards. I don't think that's the case (the seller I bought from says he got them as gifts), but you should protect yourself as best you can. I purchased the code from eBay with the credit card I'm most comfortable with potentially backing me up if I have to dispute a charge (which most credit card companies will do - but some better than others). (For many items on eBay, you can now pay directly with a credit card, rather than using PayPal.) eBay should also provide buyer support, if need be. I already applied the code successfully to my Hulu account, and worst case I figure I'd be out $20+. (Note that there appear to be more legitimate, or at least better-reviewed, sellers on eBay selling for around $30. So that's an option if you want to play it safer, and still get 70% off.)
Finally, another angle to this deal is getting Showtime for cheap. Many of you will know Showtime as a premium movie channel (similar to HBO). But they also have some great original programming, like Homeland. You can now add Showtime to your Hulu subscription for $9/month. So if you buy these discounted Hulu gift cards on eBay, you can have access to Showtime for around $2/month.
I'm new to this deal, so if you think I missed anything ... please set me straight in the comments!