Somebody: Whatever the reasons, bourgeois democratic systems are characterized by a trend towards party stabilization over time. Only in new democracies, like in Eastern Europe in the 1990's, do you see of high frequency of new political parties emerging. In the U.S. this is compounded by our majoritarian system and lack of proportional representation. The British people may be disgusted with Labour, the Tories, and Lib Dems, but it's unlikely any new parties will emerge to contest them, the same holds true in Germany, France, and most other industrialized nations.
While not perfect examples, both the Greens and the Left Party in Germany, though the latter was a preexisting formation and a fraction of another put together. Forza Italia in Italy?
(The Greens in Australia took their first Lower House parliamentary seat - Adam Bandt, who is often quoted referring to himself as a marxist, for what it is worth.)