Beginner's logic analyzer?
The Bus Pirate is probably your best bet - open source software and hardware, easy to build if you don't mind SMT, cheap if you buy it assembled ($30 shipped worldwide).

http://code.google.com/p/the-bus-pirate/

Lots of variants, with a lot of people supporting it:

http://www.google.com/search?q=bus+pirate

The bus pirate is mostly useful for serial work, though it can do some small amount of simple logic analyzer functions.  If you need to do a lot of logic analyzer work, this product looks very nice:

http://dangerousprototypes.com/open-logic-sniffer/

Open source, but has very good capabilities. Very inexpensive, though.