I've mentioned these eBooks by David Cleland from FlixelPix before. I bought them a few months ago and I enjoyed them both. In particular, I learned a lot from the Long Exposure one. I even purchased a 10 stop ND filter and have been experimenting with long exposure photography. It's awesome.
They're normally $6 each and $10 for the bundle, so this is a good deal. But it's only valid for June, so get them now. They're worth it.
To claim the discount just enter the discount code JUNE and 'update cart'.