The "tricorder" may come sooner via Kickstarter than via the Ansari/Qualcomm tricorder X-prize competition, a variety of well-connected sensors have gotten funding recently. The Public Laboratory Spectrometer is the most recent (still open, until October, but already past 200% funding) project to do optical analysis of materials; what makes it interesting is that it's taking advantage of the cellphone's builtin camera - and that they've already got a community of crowd-sourced observations and presentation tools, and some very close-to-home measurements (baseline measurements of various coffees at Tosci's :-) They've still got a way to go to connect spectra to actual materials, though they've come up with wonderfully clever tricks like using the Mercury lines from ubiquitous CFL bulbs as calibration points. (Backed)
I mentioned the IO Rodeo Educational Colorimeter Kit last week, but forgot to point out that even though they KickStarter is done, the kit is available in their online store along with a bunch of other Science! gear, like optical sensors for measuring the wing-beat rates of flies...
In an entirely different sensing range, we have the Safecast pocket open source radiation sensor - designed by Bunnie and more sensitive than most commonly available devices, with sample logging, USB download, and local display of Alpha/Beta/Gamma events. Designed in response to the Fukushima event, it could also provide interesting data in conjunction with the EPA "Where You Live" program - I happen to live a couple of miles from the Starmet Superfund Site and the more "eyes" watching such things, the better.
Mobile robot platforms using cellphones as the communication link (and local "brain") are almost mundane at this point - adding simple but sophisticated sensors to them enables a lot of interesting environmental science, with locally developed data...