Ok I second the suggestion of the Saleae logic devices.
I own the Logic 16 and would recommend it to anyone. The software it uses is really well written. It supports
several protocol decoding: I2C, Async Serial, SPI, 1-Wire, CAN, I2S, PCM, UNI/O, Manchester and MP Mode. This list
has grown a fair bit from when I was first interested in the Logic/Logic16.
Logic(8 channel)@$149USD or the Logic16(16 channel)@$299USD are both excellent choices. The come with a no hassle warranty.
Plus Customer service is probably the best I've experienced in a tech company. You would not be disappointed.
Now for the dark side, if you did want to choose a dirt cheap alternative, try googling: "CY7C68013 logic"
i.e.:
http://blog.lcdynamic.com/2011/02/logic-analyzer-cy7c68013a-core.htmlThere are several <30$ options out there using the Cypress Semiconductor CY7C68013 micro. Apparently older versions of the
Logic software will work with the boards. New revisions of the code detect clones by doing some form of latency check.
Although this option is cheap, you are in a way 'stealing' the logic software for free and the CY7 dev boards are mass produced on the
chinese markets.
All up to you, but I suggest the Saleae Logic (or 16), at least your supporting the developer for the awesome logic software they produce.
Also important to note the the Logic and CY7C68013 boards both lack input protection, and do not support several target voltages.
My 0.02, hope it's helpful.
Chris