The Hydrogen Economy
Instead of guzzling imported oil (and being at the mercy of oil suppliers) we could turn water into hydrogen and burn that (or use to charge fuel cells.) Meanwhile, the only byproduct of the combustion of hydrogen is ... more water! However, hydrogen storage remains a thorny issue, due to its low density, and hydrogen may end up being only one of many interlocking components that replace the current oil economy.
Therapeutic Cloning
Forget the stories about generating identical copies of a particular sheep or person. The whole idea behind cloning all along has been to grow replacement organs or tissue in a vat, which the body would see no reason to reject. Cancerous or damaged organs could be replaced by new, disease-free clones of themselves.
Moore's Law Upheld
The law, stated by Intel cofounder Gordon Moore in 1965, implies that available computer power can be expected to double every other year. For at least two decades pundits have been pointing out barriers to the law's fulfillment, and the chip industry has been smashing those barriers. Currently they can't agree if the law has a couple of more decades of life left, or 600 years. Either way, in terms of available computing power, it's clear that we ain't seen nothing yet.
Desktop 3-D Printing
Instead of going to the store for your next gadget, you might download a design of your choosing and generate it in your desktop 3-D printer. The next step will be to design your own gadgets, post the designs, and sell them, etc. Toys, kitchenware, and decorative household items should be fair game, at least. Cottage industry, here we come!
Location-Based Computing
Instead of clicking an icon on a browser screen, you can walk outside, point your cell phone at an actual three-dimensional thing (presumably, a building that houses a business), click the phone, and get information about (or jump to the Web site of) whatever you were pointing at. As well as servers with Internet address, there will be servers with geographic coordinates.
Better, Cheaper Solar Cells
The cost of photovoltaic cells (that turn sunlight into electricity) are coming down. In less than ten years the cost of solar energy could be at parity with the cost of electricity from the grid, and solar cells could be standard features in new residential construction. Your house could power itself about a third of the time. (Science can't do much about night and bad weather.)
Mobile Robots
The recent DARPA challenge (where robot cars navigated through suburban traffic) hints at what might come. Why drive to the deli to pick up your order when you can just send your car? We may see convoys of robot trucks on the highways. Admittedly, they'll probably have more initial acceptance in warehouses, handling pick-and-pull chores.
Pervasive Wireless Internet
WiMAX, 3G, 4G, etc., all point to a pervasive wireless Internet, where being on-line everywhere, all the time, will be routine. That implies the possibility of full connectivity between any two random devices. Want to check your burglar alarm from your cell phone? It'll be easy. Unjacking to get away and relax, however, may not be so easy.
Gene Therapy and/or Stem Cells
A lot of maladies actually involve inherited conditions—they're in your genes, in other words. But scientists are working to change those genes and trick defective cells into growing correctly. Perhaps, someday, birth defects will be as treatable as pneumonia.
Digital Libraries
Having total connectivity is pointless if all you get is the latest gossip about Paris Hilton. But the digitization of mankind's accumulated works proceeds apace. All of MIT's courses are now online, for instance, and, if you haven't done so, check out Google Book Search. The time will come when any straightforward factual question can be answered immediately, online. But, alas, those are always the easy questions.