Color sensor! This can actually detect color, what? Becky Stern has a really awesome chameleon scarf tutorial on their tutorial site, this would be great for other computational fashion pieces. This would also be pretty cool for sorting/computer vision type things.
Card readers! These look pretty fantastic, oh wow. I could see myself using these for like, a visualization of $$$ or an installation that requires users to give me money. I’ve never really messed around with card readers before though, and I’m sort of interested in seeing what kind of information is stored in the cards I carry with me daily?
When I was in middle school/early high school I was fascinated by DIY multitouch tables. I’m really surprised and pleased that Adafruit sells tiny touch screens for only $8! I’d love to make a tiny touch interface with something like this.