Well, here is a not so unlikely 2004 result: if Bush loses WV and NH, arguably outside of FL the two states he is most likely to lose, then the result is a 269 to 269 tie! No EV majority and it goes to the House, unless one faithless elector switches before the Electoral College votes in Dec.
I think tremendous pressure will be generated for one elector to switch to the popular vote winner and save us from a Constitutional crisis.
I don't foresee either an elector defecting or a constitutional crisis.
Electors are nowadays chosen very very carefully and its at least 100 to one against anyone "bolting".
As to the crisis bit the scenarios we discussed above are only if the house delegations are divided 25-25. That is not the case right now. The GOP holds over 30 state delegations so a GOP victory is all but guaranteed.
Incidentally it is the current congress not the one elected in 2004 which would decide a tie so even for those dems with hopes of a congressional sweep in 2004 it wont help you elect a President from the house.