50, it's called HR218!
But, that aside, I have my MA permit, which is recognized in: AK, AL, AR, ID, IN, KY, MI, MS, MO, OK, TN, UT.
I also have my NH non-resident permit, which is good for: CO, GA, NC, ND, WY.
I have my applications for my CT and ME non-resident permits, since I travel there, too. Instead of dealing with the common hassles of HR218, I'd rather just have the permits. That way, no detention and calls of verification to my boss at 2am to verify employment.
I've also considered getting my non-resident FL permit, which will also add: LA, PA, SD and TX.