1. Pamplona Running of the Bulls
This is the big one. Every morning at 8am during the San Fermin festival, thousands gather to see the main event - large numbers of men running in front of a pack of angry bulls. If you don't have a balcony to watch the bull run from, be sure to arrive early to get a good view. The entire run only lasts a couple of minutes and the stretch that you see will be over in under 20 seconds, but no matter - there is a bull run every day for the duration of the festival (that's eight of them!).
Read more about the Pamplona Running of the Bulls
2. Running of the Nudes
Read more about the Pamplona Running of the Nudes
3. The Running of the BusesPamplona's infrastructure comes to a standstill during the San Fermin Festival, and that includes the public transportation system. So when the buses leave the depot again on the first morning after the festival finishes, the San Fermin hardcore do one last run 'for the road', allowing themselves to be 'chased' by the buses as they take to the streets again.
4. Running of the Red BullsA one-off PR stunt by the Red Bull F1 team saw Formula One drivers David Coulthard and Mark Webber chase people through the streets of Pamplona shortly before the 2008 San Fermin festival. I understand that the locals weren't interested in their festival being used in this way (because the festival is in no way commercialized at all, of course), so actors had to be brought it for the stunt.
5. Running of the Cows
Equality for the sake of equality or a genuine desire to get in all the fun, the call for a 'Running of the Cows' resulted in an article in El Mundo, one of Spain's main newspapers. Nothing came of it, but I wouldn't rule out a "ladies' day" At a future San Fermin festival.
Read more about the Pamplona Running of the Cows