Mutually intelligible languages?

 Partially in response to the previous post... I'm wondering what languages are mutually intelligible.  As a native English speaker this is an interesting concept, because there really are no languages close enough to English to just listen and understand.  However, I know that a lot of Spanish and Italian acquaintances can converse without problem, and I'm able to use my Spanish to understand Portuguese (at least, enough to watch their version of Are You Smarter than a Fifth Grader and feel pretty smug)

So, other than Spanish/Italian and Spanish/Portuguese, what other languages are mutually intelligible?  What languages are YOU able to understand, even though you've never studied them?