I was excited to see these free resources and perhaps use them and/or link to them on my website. I have feedback for Dave, though.
Dave, you have put so much work into this site, and it's very usable. Great programming.
I wouldn't use it to teach or practice math facts, though, and here is why:
The problem practice consists of mixed-up problems. Yes, they are separated by size of number, which can be useful and better than many worksheets out there. (The downside is that ordering it like this can imply that larger numbers are "harder" than smaller numbers.) However, I learned a few years ago that the best type of worksheet is designed like a sprint, which Yoram Sagher invented. This is a sheet of math facts practice that teaches at the same time. For example, you might see the following problems:
5 x 9
50 x 9
500 x 9
5000 x 9
or
6 x 5
7 x 5
8 x 5
9 x 5
5 x 6
5 x 7
5 x 8
etc.
In other words, you are providing the opportunity for students to notice patterns for themselves and get very fluent in mental math facts by applying these patterns. Randomly ordered math problems don't offer this.
If you were to offer more sprint-like practice, I would be THERE in a minute. It's a lot harder to create these, though, which may be why there is only one offering out there on the marketplace.
Beemath looks like worksheets that could just as easily be sent home on paper. Ideally, a math website offers practice that can't be done on paper, like
http://www.thinkingblocks.com.
algebrafree.com looks promising for students without access to a teacher and/or supplementary practice.
Thanks everyone!