Here is what we do and it goes over great:

1st time: Free
2nd time during your turn: pay 1 life
3rd time during your turn: pay 2 life

etc. 

Try it!

I am so glad I found this post!  I will add my two cents from what I have seen...  (We T4 in between rounds of drafting at FNM and its a blast.)

Any library searching I have tossed as it just takes too long. (Academy Rector/Black Bringer etc.)

We also play 'one creature and one non-creature' spell per turn.  Try it!  We find it is much faster and more interesting not only in two player but also multiplayer!  (It also makes creatures with flash like B. Hellkite even more amazing as you can also play an instant on opponents turn)

Thanks for your lists!  I will add mine when I get some time, but its over 500 cards and many have already been listed.  The new 'sac a creature, draw' artifact from Zendikar is really good (I know its a reprint with a different name).  Its great with things like Storm Herd obv. and against wraths.