I've found Monoprice quality to be hit-or-miss by product. Their speaker wire is a fantastic bargain, I ran two systems with them, including a pair of the bi-wire cable (yes, it's really being used bi-amped), and a whole mess of their screw-down banana plugs on every termination. Great stuff.
Their HDMI cables, I would require them to pay me to take them again. I've had nothing but trouble from them. I've had four of their CL2 HDMI cables break under their own weight (meaning I didn't move them around at all after setup.) This resulted in numerous incidents of thinking my DVD player or AVR had broken and fiddling with the wire for an hour to get it running again. Their flat CL2 HDMIs seem ok though (different vendor?) as are the HDMI "pigtails."
Their HDMI switches, while sometimes featuring an ungainly interface and dreadful remote controls are well made and second to none.
Their analog audio video cables come in two varieties: low gauge and sad (the stuff you get for free with every DVD player), or the Premium which is good stuff, but generally features cheap jacketing and cables that are stiffer than they ought to be. It's fine for running once, but I don't like the pressure it puts on jacks and tends to leave a messy cord maze that looks something like a Borg contraption. Their premium digital audio cables seem ok.
I recently bought a different brand of power cords for my Schiit gear (I needed shorter, right angle cords.) The pictures of the Monoprice ones looked suspiciously like the ones included with the gear. While just fine power cords, electrically, I noticed they weren't quite to IEC spec for the jack and as such had a little bit of wobble room and I suspect could accidentally be removed if tugged on by mistake. The C2G one I bought instead was only slightly more expensive but fits the IEC jack snugly without wobble. It's also a more flexible jacket.
Performance wise most of their stuff is fine, but sometimes their build is either suspect, or ungainly, so it pays to shop around. There are other good industrial cable companies out there that aren't quite as bottom-of-the-barrel cheap as them but are in a similar "wholesale" pricing bracket and, IMO, sometimes use better materials.
I do like BJC for more important things though, so I'll second that, and I recently learned they carry some stuff that isn't always posted on the website. They are much more expensive (but far from designer), but I must say that the Belden cable is remarkably well built (and in most cases, it's outdoor rated so it has to be.) That won't help for USB though!
Edited by IEMCrazy - 3/7/12 at 12:29pm