The Topology Atlas is a huge database of (mostly researchlevel) information on topology. It includes a page of lecture notes in topology, for example. There is a fairly wide ranging discussion of General Topology (i.e., pointset topology), which is part of a larger group of pages on the various divisions of mathematics. More generally, there is the rather entertaining Interactive Mathematics Miscellany page. My favorite little tidbit so far has been "[By the extreme value theorem,] for any object there is a distance at which it looks its best." (It took me a little while to figure out why that was actually true.)
