How to select a good quality Duplex Outlet . . .?
Receptacle grades 101 (for North Americans)

As you have noticed, North American wiring devices, such as receptacles and wall switches, come in multiple grades, each with an associated pricetag.  While there aren't hard standards on what each grade means until you reach the upper echelons, most manufacturers have settled on a basic system that goes like follows, from cheapest/chintziest to best built/tested:


Builder or residential grade.  These are the $.59 outlets that you find on special at the big-box stores, and are also what are used by builders wiring tract houses (in order to keep prices down).  As a result, while they meet the UL specification for receptacles, they generally just slide by, instead of exceeding it by a large margin.  However, they can give acceptable performance over time for a lightly-used receptacle if wired using properly torqued side screws.  Just don't use the "backstab" wiring features these receptacles provide!
Specification or "spec" grade, also known as commercial or construction grade.  This is the next step up from a builder-grade receptacle, and generally cost $2-$5 a piece.  These receptacles ditch the dreaded "backstabs" in favor of using a screw-and-clamp backwiring system that does a far better job of holding wire, in addition to generally being more robust.  They're what you'll find in places like office buildings, schools, and such, although they certainly are not out of place in a residential setting either.  They also offer a broader variety of options (receptacle types and so forth) than builder-grade parts do.
Industrial (heavy-duty) grade.  These are the next step up from a spec grade receptacle, and are found in industrial environments and other highly abusive places, as their name implies.  As a result, they have extra-high-impact plastic parts and improved contact systems over their spec-grade counterparts, in order to withstand not only mechanical abuse, but industrial-level electrical abuse as well, such as repeated motor surge currents.  This is where you get into paying $10-$20 a receptacle, as well.
Hospital grade.  Finally, we get to the beasts of the receptacle world, those meant for some of the roughest use possible: hospitals.  Hospitals are notoriously rough on equipment, and also place high demands on the safety of electrical equipment due to just how vulnerable you are to being zapped when you're opened up on an operating room table.  As a result, these receptacles receive extra abuse testing as part of the UL listing process in order to get their Hospital Grade designation, and will be marked specially with a green dot on the face in order to denote them as Hospital Grade parts.  Interestingly enough, they aren't as costly as industrial grade parts, either, only running somewhere in the $5-$10 range.


(You'll also run into what are called Federal Specification, or Fed Spec, wiring devices; these are basically something that's received a bit of extra UL testing to make sure it meets the standards the US government has set for the receptacles it puts in its own buildings.  Generally, any decent commercial/specification grade receptacle should be Fed Spec as well, although not all are.)