This guide looks like a great resource for learning about DSPs and how they work. While there is no getting around some of the math, the explanations and diagrams are excellent. It also has an interesting chapter on Benford's law; why one is the most common leading digit for some types of data. If you want to avoid wasting ink in your printer you can also buy a hard copy of The Scientist & Engineer's Guide to Digital Signal Processing.
On the applications side the TI OMAP is pretty interesting with the Gumstix and Beagleboard both being popular platforms for GNU/Linux based robots. One of the most interesting features is the built-in DSP, which is useful for computer vision tasks or just for accelerating gstreamer. This should be useful for encoding video telemetry data, until someone develops an ASIC or FPGA solution for encoding WebM. Another alternative to avoid composite video may be to wait for WirelessHD.