My first find was the Quick Reference: Google Calculator (Cheat Sheet).

I like this tip from Google Guide solutions to Calculator problems:

Compute the probability of your winning the lottery if you buy 1,000 tickets each bearing five distinct independently randomly chosen integers between 1 and 99.

The following answer was contributed by Nelson Blachman (Nancy’s father).

You might try [ 1 – (1 – 1/(99 choose 5))^1000 ], but this is well approximated by [ 1000/(99 choose 5) ], which is roughly 0.00001 . If each ticket costs $1, the prize had better be at least $100 million to be fair to you — and higher if you might have to share the prize with other winners.

Also… I've always wanted to figure out the probability calculation for various poker hands.

One more interesting link: Soople.com's Visual Interface to Google's calculator