My 7 (soon to be 8) year old boy does this too... more often at school then at home. We make him leave the room if it happens at home, putting him on his bed - and we only point toward the stairs when this starts and he knows he's excused and not to return until his fit is over... he gets angry about this because he's loosing the attention he wanted... at school they're not as creative, or as consistant - as a result, he's in BED program - I'm sure you know what this is from teaching...
I suggest forming an agreement with your husband on what to do each and every tantrum, and you must create a solution that works both in and out of your home. So that EVERY time this happens, he gets the same boring result. It will take ALOT of consistancy on your part, and your husbands - and if your husband is like most men, this is excrutiating... to punish his child constantly he will feel like the 'bad guy'... but in the end - you must tell your son that you love him too much to allow him to act that way, and you should also get an apology from him for his actions each and every time. We use reward programs at home too.
ODD is a possiblity, and I'd see a child therapist if it persists, play therapy does wonders for them even if there's no deep issues - it allows them to vent. Something they may feel is 'wrong' to do with you and dad.
Another mom wrote to buy "the expolsive child" - and I suggest that as well!
I've learned that it's always HOW you react that will either promote or reduce his behaviors, our silent pointing to our son says "what you're doing is unacceptable, and I will not talk to you right now - go calm down" without even saying 1 angry or harsh word to him. It's excusing him to another room to act out his issues if he needs too - and if he makes a mess doing it, by throwing things in his room - conseqence will be to clean it up!!!
Good luck, and I'm sure you're doing an awesome job!