There are a variety of over-the-counter commerical products you can buy that help dissolve and break down sewer blockages, be they in sink drains or toilets.
Chances are the blockage is in the toilet itself, not the sewer pipe beneath it. You can snake the line with anything flexible (hell, depending on the toilet you can probably get a bent coat hanger through the neck), or shut off the water supply, drain the tank and the bowl, and unbolt the toilet from the floor. A pair of gloves and something to block the smell will let you extract the blockage from the bottom. Just be careful if you use this trick, there's a wax ring that seals the toilet to the sewer pipe and you DO NOT want it to get damaged.
Or plunge harder
You realize the bowl should be quite full of water when plunging, right? You need the hydrostatic pressure to dislodge the blockage.
Good luck =)
