Thesis writing phase is almost over, we expect a return to normal blogging activities within a few weeks.
Books on music theory intended for mathematicians is a question on MathOverflow with a wealth of interesting book suggestions. On a not completely unrelated note, I am at the moment also working on my final project for my harmony and composition course. It involves fugues and the guitar, and I'll discuss it a bit on my blog soon.
Some professors' home pages contain a wealth of interesting lecture notes. It's not a secret that Brian Conrad's is one of these, but his lecture notes on linear algebraic groups deserve a special mention. Likewise there are Paul Garrett's on buildings, BN-pairs, Hecke algebras and algebraic groups.
If you like mathematics and stamps, check out MathStamps.