Here are the lecture notes from 18.310 in fall 2010. The topics in fall 2011 may be rearranged in order; some topics will be different, but most will be the same. Some of these lecture notes need work, although many are in what I think is good shape.
Batcher's algorithm lecture notes
Probability (part I) lecture notes
quicksort and randomized median finding notes
Probability (part II) lecture notes
Shannon's noiseless coding theorem
generating function notes from 2005
Algebra, GCD and Chinese Remainder