There's a few solid free books on algorithms, but I'm not aware of anything comparable to "Concepts, techniques, and models of computer programming" by Peter Va

There's a few solid free books on algorithms, but I'm not aware of anything comparable to "Concepts, techniques, and models of computer programming" by Peter Van Roy and Seif Haridi available for free, (besides SICP and HtDP) so my advice is to check it out and then buy it.