I've got a repo on github.com
I'd like to get a delta of two random (non-sequential) commits.
How can I do that?
Preferably on the site itself.
Github has a help article exactly for this: https://help.github.com/articles/comparing-commits-across-time/
TL;DR: Go to your Github URL for your repository which will be in a pattern like http://www.github.com/<user>/<repo>
then add /compare/<commit1>..<commit2>
where your commits are the start of the hash code for the commit.
A note on the hash codes: Git hash codes are actually 40 character SHA1 hashes, but you can "shorten" them and Git will try to find the commit that starts with what you've put. On Github, they standardize on putting 7-character codes, but this functionality still works (so a hash of 27e515f54a4757... can be written as 27e515f). It seems the shortest you can go is 4 characters before it stops working, and obviously if two hash codes start with the same characters, you have to give enough for it to be unambiguous.