Hmm, have you tried a restart of the computer? I would also try a soft restore of teh iPhone (holding down both buttons until the iPhone restarts). I would think then the computer should recognize the phone, because it's not a problem with the iPhone since iTunes is recognizing it.
Is there a default option where when you connect a camera it tells iPhoto not to open when an iPhone is connected? Maybe this option was accidentally selected. I guess you could just manually open the iPhone through iPhoto and then it might recognize the iPhone again after that.