Sensor needs to be cleaned. I clean every six months, on average, but MORE often in the summer time months, when I shoot more outdoors, and there tends to be a lot more junk in the air than during the winter and spring months. My recommendation: do not use too much cleaning fluid on the sensor swab! I like Eclipse brand fluid for my cleaner. I bought a bunch of no-name swabs from eBay a few years back.
Dust spots like those shown above get to be a PITA, especially if you want to be able to shoot at f/7.1 down to f/13...at smallish lens opening sizes, the dust spots are problematic. One drop of fluid on a swab, and then two passes each, with two consecutive swabs, would clean this mess up. If you shoot more at wider apertures, like f/2 to f/4.8 or f/5.6, the dust spots will tend to be more-diffused, and less-black, and will "clone tool away" reasonably easily. Still....you can SHOOT CLEAN images, or be forced to clone away multiple spots. One remedy means five minutes' worth of work, while the other means hours of hassle. The choice is up to the individual camera owner.
At times, dust spots are a big deal; on some subject matter, dust spots are a real, significant problem, on other types of subjects the spots can be very hard to see.
On newer, higher-resolution sensors, dust spots seem to be MORE of an issue than they did years before, so KMH's never needed to clean a sensor comment makes sense for its time; I noticed the same issue on my earlier D1,D1h, and D70 and S2 Fuji d-slr cameras; at LOW resolving power levels (6MP or less), dust spots seemed to be a lot less noticeable than they do now, on 24-million-pixel images.
Use the mirror lock-up function in the menu, blow the sensor off first with a bulb blower (NOT compressed air), swab a couple of times as Derrell said.