To keep track of my running distances and timings, I logged my data to mapmyrun. I was not completely satisfied about it, due to slowness, some bugs, pervasive ads and the difficult process with which to do simple things (adding loops, adding intervals etc). They also recently changed their layout (which they appear to do more, according to some forums).
That was a good enough reason for me to look for an alternative. After trying a couple (gmap.pedometer.com, walkjogrun.net, mapometer, runningmap and runningahead.com), I decided to stay with runningahead.com.
It is fairly quick, has a clean layout, allows export and import of data, and I understood most functionality quite quickly. It's log capabilities are advanced (having several types of intervals, equipment used, activity type, weather), and its map editor works like a charm and is stable. It also seems to have quite a good customizable analysis tool, like a community built around it. But I haven't tried both yet.
runningahead.com is completely free, yet there are some ads shown on the page that disappear upon subscription.