For basic FEM concepts on Matrix methods, I really like McGuire, Gallagher, and Ziemian's book "Matrix Structural Analysis". Now, it is almost exclusively frame elements. But, it does a really good job introducing shape functions, 2nd order effects and such.
For more complex concepts I tend to look at a few different references. Ed Wilson's book is good for dynamics. KJ Bathe's book is good for plate and shell element formulations. There is also a book by MacNeal that offers a good discussions on various types of elements and where their weaknesses are.