I'm trying to find some really nice sharp thunder cracks, but it's quite difficult to find good ones. Any tips on how to either make one or a good small affordable library with some good ones. I'm looking for quality over quantity
Check out these libraries from therecordist.com.
His technique and equipment are top-notch. The quality of his libraries are excellent.
If you need it on the spot, or in fact, anytime soon, go with a library. The Recordist libraries are, as @Airborne says, pretty great. If you have (a lot of) time, I'd suggest recording your own. You have to take storms as they come to you, but it's worth it.
I've found that pretty much every thunderclap has a different character to it. I uploaded a couple of plain examples to soundcloud a while ago. Both have come in handy for me: http://snd.sc/10ojN9j and http://snd.sc/YKZfee
Check out my rain and thunder collection. There are a bunch of nice thunder hits. Hope this helps.
Weather Sounds: Rain Hail and Thunder
Sound Effect, Pack 14A Weather Sounds: Rain Hail and Thunder
The pack of 112 sound effects is just $6-95. Not all of the sounds are thunder. The pack also includes rain and hail...but there's plenty of thunder in there too.