BBC has great explanation of us
If you're like me and not entirely sure you understand the whole caucus versus primaries thing and where the contests are all being held and when, the BBC has explained it very succinctly at http://news.bbc.co.uk/.
Assuming that Europeans may not understand how it works they have come up with an informative Q&A and interactive map of the US that I found simpler and more direct than anything I've seen in a U.S. media outlet. If you go to the site today, click into the analysis of the Obama win in South Carolina and a whole menu of U.S. political news options will be in a menu on the right including how the process works.