There are some things over at divmod.org which I'm pretty sure should be part of Twisted.
The templating system from Nevow - the newest one, without the context, without any deprecated junk, should be imported. Twisted wants to generate HTML in a few places - error pages, the directory listing - and right now it either gets it wrong or the implementation is a disaster or both. We should replace them with something based on this templating code. It should also be generating HTML in a few more places; like, perhaps an admin UI to allow an admin to instantiate new resources, and I'm pretty sure we are avoiding at least a couple of useful bits of functionality on the basis of how incredibly nasty and difficult it is to generate some simple HTML without adding a mountain of new dependencies (which, of course, wouldn't support Deferreds).
The resource model from Nevow, which is slightly more advanced version of the one in web2, should be imported.
nevow.guard is basically just a more advanced version of twisted.web.guard, and should be imported, probably after the resource model upgrade.
Pretty much everything in Epsilon, I think, should be in twisted.python. Especially extime.Time, which would make the various things in Twisted that need to parse dates simpler and more consistent.