A: This is one of my oldest patches - it's for the AMC (Appalachian Mountain Club) which maintains all of the hiking trails and huts I use in the White Mountain National Forest. I think they changed their logo last year, so someday this patch will be an antique! :)
B: This patch is the logo for the Raspberry Pi, which is a single-board computer that can run Linux, and only costs about $25. I use them in many of the projects I've posted on this blog - including the Pandora Radio, the Emulation Station, and the RPi Photo Booth.
C: This patch is the logo for the Arduino, which is the *other* single-board computer I use on my projects. The Arduino is lower-level, and doesn't have an operating system. It makes some things easier to do than the Raspberry Pi, and some things are harder. So they are each better suited to different projects.
D: This waving robot is the mascot for Adafruit, the company that I get most of my parts from for all of my electronics projects. They've got tons of components for sale, plus oodles of tutorials and example projects for everything they sell.