damn, usually this is done in conjunction with a plunger.
get a bucket. fill with HOT water, and pour into the toilet bowl. keep repeating. in the words of my apt manager, it will "act as an agent" and it somehow unclogs it. it works. eventually the water will go down completely as you pour it in and you should be able to flush again.
although this is usually done in conjunction with plunging, but its worth a shot.
it must be a decent sized amount of water you're putting in, not a little bowl's worth.