When Dr. McCoy on Star Trek aims his medical tricorder at a patient, it tells him exactly what's wrong within seconds. Of course, that's in the 23rd century. In 2010, we have the Lawrence Livermore Microbial Detection Array (LLMDA), a $500 device that scans a sample on a glass slide and tells you which viruses and bacteria are present within 24 hours. Not bad, considering.
The array has 388,000 tiny probes in a checkered pattern on a 3 x 1-inch glass slide. The probes can detect any one of 2,000 viruses and 800 bacteria. That's super-useful for medical forensics and even biodefense, since current techniques identify only 50 or so pathogens at a time.
The lab is already working on a next-generation array with 2.1 million probes, enough to detect 5,700 viruses and "thousands" of bacteria. Now if we could only get at-a-distance scanning and instant analysis, then we'd have Starfleet's favorite medical tool.