Cree
Cree is a LED manufacturing company based in Durham, North Carolina. They produce high output LED's from their XLamp LED series that are widely used in flashlights.
Cree bins individual models of LED on the basis of total flux or light output, typically measured at 350mA. Bin numbers might be P4, Q2, Q3, Q4, Q5, R2, R3, R4, and R5 with each bin being about 5% additional flux. The P4 is 80 lumens, a Q5 would be 107 lumens, and the R5 bins are 137 lumens. At higher amperage than 350mA, the brightness goes way up, with the XP-G producing 3 times as many lumens at a maximum current of 1500mA.
Cree classifies tints generally as being warm, neutral, and cool, but has recently added "outdoor white" in between neutral and cool (or as a replacement for cool?). Some LED's, such as the XP-E, XP-G, and MC-E are now sold binned by ANSI tints, such as cool 1B, neutral 5B1, and warm 7D2, though many other tints and subdivisions are available. The chart is available at this CPF post. Those tints are in addition to the brightness bin.
MC-E
A 4-die LED available with four of the same color dies or the MC-E Color with four different color dies (white, red, green, blue). The maximum current is 700mA with a Vf of 3.4V, though this varies from one color to another. Bins run from G (240 lumens) to M (430 lumens) at 350 mA. The white quadrant of the MC-E Color is available in cool white (A5) or neutral white (A4).
The MC-E is widely used in high-power flashlights like the EagleTac M2SC4, Fenix TK40, iTP A6 Polestar, and JETBeam M1X with advertised output of up to 700 lumens. The color version is in the Quark RGB (with neutral white or cool white available) but although the LED allows mixing of colors, the Quark RGB is switched to one color at a time.
XM-L
Larger die LED announced in April 2010 and first available in November, offering efficiency of 160 lumens per watt at 350mA. Output is 260-280 lumens at 750mA (bins T5 and T6) therefore it is more efficient and puts out more light at any current than earlier Cree LED's. However the biggest improvement to overall output is the XM-L can be driven to 3000mA for 910-975 lumens of output. The LED die is 2mm x 2mm on a 5mm x 5mm substrate with 6 yellow strips and 3 bonding wires as opposed to the XP-G with 4 strips and 2 bonding wires and the XP-E with 3 strips and 2 bonding wires. The first production lights to feature the XM-L were versions of the ThruNite Catapult V2 (first to ship), EagleTac M3C4, a 4Sevens Quark MiNi, and the JETBeam M1xm, introduced in December 2010, but budget retailer KaiDomain had LED's and P60 drop-ins as well as P60 lights around the same time. Press release Cree XM-L datasheet
XP-C
A lower current version of the XP-E with a smaller die. Maximum current 500mA and Vf of 3.5V. Bins up to Q4 (100 lumens) in cool white, Q2 in neutral white (84.7 lumens) and P3 in warm white (73.9 lumens). Looks like the XP-E, but the die has 2 yellow strips and 1 bonding wire instead of 3 strips and 2 bonding wires.
XP-E
Introduced in Fall of 2008, the XP-E shrunk the XR-E by 80%, now 3.45 mm square. It is available, in white (cool, neutral, and warm), blue, green, amber, red, and red-orange. For cool white, bins are Q3, Q4, Q5, R2 and R3 with output from 93.9 to 122 lumens. Neutral white bins are from P4 to Q4 (100 lumens min) and warm white bins range from P2 to Q2 (87.4 lumens min).
This LED is used in the Nitecore Defender Infinity, early Quarks (R2, neutral whites used a Q3), the iTP A series EOS and S series lights, EagleTac P100 and T100 series.
This CPF post allows easy identification of the XP-C, XP-E, and XP-G LED's. The XP-E has 3 strips on the die as opposed to 2 on the XP-C and 4 on the XP-G.
XP-G
Same size package as the XP-E, but with a larger die. Therefore the resulting beam has a little more flood. It is available in varying output bins from R2 to R5. Maximum current is 1500mA and Vf of 3.3V with efficacy of 132 lumens per watt.
The XP-G R5 began widespread use in 2010 after being adopted early by 4Sevens and EagleTac. The R4 was used in limited edition titanium Quarks and some of the latest Fenix lights. S2 bins became available in November 2010 but only in Quark and iTP special edition lights. 4Sevens made 100 MiNi 123's in titanium with S3 bins in December 2010.
XR-C
Same size as XR-E (7mm x 9mm) but is designed for less current (500mA max). The die itself is smaller than the XR-E. The maximum bin is Q2 with 87.4 lumens for cool white. It is available in white (cool, neutral, and warm) as well as royal blue, blue, green, amber, red-orange, and red. Vf is 3.5 volts at 350mA. Identifiable by the metal ring around the dome and a LED die with only two yellow strips and one bonding wire.
The XR-C is used in retail lights made by Coleman, River Rock, and Energizer.
XR-E
Introduced in the Fall of 2006 the XR-E is widely used in a number of different flashlights, with cool white, neutral white, and warm white colors available in addition to blue, royal blue, and green. Common bin numbers are P4, Q2, Q3, Q4, Q5, and R2 with increasing output from 80 lumens to 122 lumens at 350 mA and a Vf of 3.3V, but with much greater output available with higher currents. The size is 7 mm x 9 mm and you will often see this referred to as a 7090 XR-E.
This LED is very widely used, featured in flashlights by Fenix, JETBeam, NiteCore D10, and EagleTac P20 and T20 series. The neutral white version is used in Nitecore EZ series. It is easily recognized by the metal ring around the die with 3 yellow strips and 2 bonding wires.