If you haven't re-centered and/or adjusted your bike's brakes lately, now is the time. I found my pads were dragging a little.
Basically, if you clamp the brakes, release, and the wheel won't spin freely without stopping for 20+ seconds, then it needs to be fixed.
Cantilevers have tension screws at each post to re-center them. There's a barrel adjuster for gap.
Calipers just unscrew the center screw half way, clamp the brake lever, and tighten the screw before letting go. Magic, I know. They also have a barrel adjuster for gap, but there's also a cam on the side (for wheel removal).
If your pads touch the rubber, or are not in the same place on the rim at both tips of the pad, then that needs adjusting too.
If your brakes are not dragging, and the wheel still doesn't spin for a long time (on the bike), then your bearings are gunked up. If it's a cheap wheel, replace it, or have fun taking it apart. If it's an expensive wheel, then have it serviced at your local bike shop.
Speaking of expensive wheels, I got some EA70 road wheels.. I know, in the grand scheme of biking, these are still cheap, but they are a massive upgrade for me. In reading up on maintenance, I found that wheel truing is different for these. Easton tightens all of the drive-side spokes to maximum, yet even tension. THEN, they tighten up the non-drive-side spokes to obtain the proper dish.
If you need to do anything to the drive-side spokes, you have to de-tension the entire wheel first, do your thing, and then re-tension it the same way they do. If you don't, you'll break the spoke nipples due to them being at a higher tension than you can actually set by hand. Also, Easton says, at least for their wheels, even tension is more important than 1-3 thousandths wobble.
Also, they have no weight limit for their wheels (stated clearly on their website) and they have a 2 year warranty against defects. If you hit a pot-hole and dent/bend/break the rim, tough patooties. But if you ride over a little crack and the wheel breaks or tacos because you're too heavy, they will take care of it (through your LBS or through them, but not for ebay or random-internet sellers).http://omnitech.net/xaminmo/2014/03/08/rolling-resistance-is-more-than-just-tires/