data structures and algorithms e-books
By far my favourite algorithm textbook is The Algorithm Design Manual, by Steven Skiena. Very easy to read, very practical, and extremely useful. The first half of the book is a general treatment of algorithm theory, with lots of practical examples. The second half is a huge library of common problems, what algorithms can be used to tackle them, and comprehensive lists of references. You won't be disappointed.
I like Robert Sedgewick's Algorithms books. The original one used Pascal and is nice because it does not get boggled down in language issues.
Concrete Mathemetics - By Donald Knuth (understanding the math behind algorithms)
I don't know if e-book versions are available for these, but if they are...these books will definitely give you the theory behind worst-case, and asymptotic analysis of algorithms.