Protection: Chocks, Nuts, Stoppers, hexs, Cams, pitons...

Thin-crack protection:

Type	sz	Crack sz in.	kN
R.U.R.P. ( Realized Ultimate Reality Piton)	1	1/16	?
Knifeblade/Bugaboo piton	1	1/8	?
CAMP Ball Nut	1	1/8 - 1/4	8 kN
Black Diamond Micro stoppers	#1	.15	2 kN
Wild Country Cam	Z1	.22-.31	3
CAMP Tri Cam	0.125	.4-.6	3

kN - kiloNewton = 225 lbs
See also: Peckers
Black Diamond Micro Camalots vs Colorado Custom Hardware (CCH) Aliens

Note: Leader falls can generate forces in the range of 7kN, so these devices are not designed for this kind of protection unless used in combination.
The above forces are for failure of the device; Bad placement or the condition or type of rock can cause failure with much lower forces.
Camming devices "fail" regularly, but it's seldom the fault of the device. It's more likely due to haste, coupled with undeserved faith in technology.

Terms/Manufacturers:

backcountry.com
BD Black Diamond
C.P.M.P.
CCH Colorado Custom Hardware
EMS Eastern Mountain Sports
HMS Carabiner: Halbmastwurfsicherung carabiner (Pear-shaped)
PETZL
REI Recreation Equipment Inc
rockclimbing.com
RURP Realized Ultimate Reality Piton
SLCD Spring Loaded Camming Devices
See also Glossary at the main climbing page.

Links:
ADS Catalog (pdf)
Gear for rescue
Gear Selection at WildCountry.com
Ropes
Rope System Analysis - an analysis of the loads in a typical climbing rope system subjected to a dynamic loading from a fall.
Trad Gear at Spadout.com