+1 on all of those books. If you are interested in multi-dimensional indices (R-Trees, M-Trees, and many more exotic ones). You should checkout "Foundations of Multidimensional and Metric Data Structures" by Hanan Samet. Very comprehensive! "Database Systems: The Complete Book" is fantastic (pick up the previous version it is cheaper!) but it only touches on multidimensional indexing.

Also if you are interested in B-Trees start with "The Ubiquitous B-Tree" by Comer. [ http://dx.doi.org/10.1145/356770.356776 ].