A *(Learning Lounge) course about _(semantics) for _(programming language)s.

Matthew Hennessy: <a href="http://www.cogs.susx.ac.uk/users/matthewh/semnotes.ps.gz">Semantics of Programming Languages</a>.

Andrew Pitts' <a href="http://www.cl.cam.ac.uk/Teaching/2000/Semantics/">course material</a>. 

Hanne Riis Nielson and Flemming Nielson: <a href="http://www.daimi.au.dk/~bra8130/Wiley_book/wiley.html">Semantics With Applications: A Formal Introduction</a>.
 