Our monthly meetings usually consist of a talk about some aspect of Linux or something relating to Linux. Here you will find links to overheads from previous talks. Please bear in mind that all material available from here is copyrighted by the respective authors.
Andrew Bulhak - the Postscript language You might also like to look at the source for this, as it is quite readable postscript, and shows Andrew's system for making Postscript overheads.
Mike Battersby - writing a character device driver. These are probably very out of date by now, but might be a good starting point if you're interested.
Also, check out the overheads page at the SLUG web site.