I enjoyed reading 'Concrete Abstractions', and it's usually very cheap if you buy it used on Amazon (I think I paid about $5.00 for a copy that was like new.)

I disagree with the recommendation for 'Simply Scheme', though. I didn't learn much from it, and I was disappointed with the amount of code in it that was non-standard stuff created by the authors purely for pedagogical purposes. I would personally recommend spending more time on HTDP or SICP instead of reading 'Simply Scheme.'

This is a noteworthy objection, and applies to much of Harvey's course at Berkeley as well. I think the rationale for his approach is so that student's don't get tripped up by using only math examples.

Several people have brought up HTDP, which is very much in the same SICP-inspired vein as these other books in the list. I personally find it to be different enough from SICP as to not be considered a precursor to SICP. YMMV.