Memory Craft is great.
In addition to those, anything by Dominic O’Brien is good for beginners. I liked the Quantum Memory Power audiobook when I started. If you don’t already have an Audible account, you might be able to get it free here.
If you haven’t already seen our free ebook, I’d recommend reading that first, because it’s short and provides an overview of many memory techniques. The other books (and the wiki/forum here) go into more depth.
For anyone looking for it, On the Shadows of Ideas is available here.
Also, check out this page: