Date, math, time, hash (and the older md5, etc) are good starters. The
XML related libs would be good to have, but they might prove weighty
and difficult to port over (in the short term picture at least).
Pyjamas seems to have made some good choices in what they've
implemented so far. They did a little research for us by finding out
what is commonly needed when trying to use Python in a browser
environment.