Below are some links for 26650 batteries. Feel free to add posts and I'll incorporate with this list in the future. I am making no claims or endorsements as to quality, but if you have links to actual tests, please let me know and I'll include here. Any information you come across related to new cells or chemistries - please share in this thread. after the name denotes suspected capacity inflation by seller - believe at your own risk.
King Kong INR 4000MAh: International Outdoor Store $9.47 - Li(NiCoMn)O2.
King Kong INR 4000MAh (Raised Top): International Outdoor Store $9.97 - Li(NiCoMn)O2.
King Kong ICR 4000mAh: International Outdoor Store $8.97 - LiCoO2.
King Kong INR 4000mAh: CN Quality Goods $8.50 - Li(NiCoMn)O2.
King Kong ICR 4000mAh: CN Quality Goods $7.90 - LiCoO2.
*** Note on King Kong batteries *** Description with ICR26650E on wrapping are typical Li-Ion chemistry: Lithium Cobalt - LiCoO2; Those with INR26650E are Lithium (NCM) Nickel Cobalt Manganese - Li(NiCoMn)O2. If you are using these in multi-cell flashlights, do not mix the two types of batteries. See post #60 for discharge test of ICR26650E version and here for test/review. See this thread for review of INR26650E. Flat top versions may require a magnet or other spacer in multi-cell applications. Note that both versions of KK cells have tested well above rated capacity.
Knot Top 4000mAh: CN Quality Goods $8.50 - LiCoO2.
Lighthound 3500mAh: Lighthound $9.99 - These are Lithium-Manganese (IMR) cells.
Powerizer 4000mAh: Batteryspace $9.95 - These are Lithium-Manganese (IMR) cells.
Powerizer 3600mAh: Batteryspace $9.50 - These are Lithium-Nickel-Cobalt Manganese cells. Discharge Test here.
MNKE 3500mAh: International Outdoor Store $9.35 - These are Lithium-Manganese (IMR) cells. Out-of-Stock.
MNKE 4000mAh: International Outdoor Store $9.95 - These are Lithium-Manganese (IMR) cells. Out-of-Stock. Steven Wallace reviewed this battery here.
Tenergy 4000mAh: All-Battery $11.99 - LiCoO2.
No-name Blue 4000mAh: Buyincoins 2/$15.08 - No information, use at own risk.
4Sevens 3900mAh: 4Sevens $14.95
Trustfire 5000mAh: Manafont $13.33 - Actual capacity is +4500mAh. Benkie's Discharge test here.
Trustfire 5000mAh: Buyincoins 2/$22.89
Trustfire 4000mAh: CN Quality Goods $11.50
Trustfire 5000mAh: Dealextreme 2/$22.80 - Actual capacity is around 4200mAh. HKJ's Discharge test here.
Aliexpress 4500mAh: Aliexpress 2/$19.99
MarsFire 5000mAh: Manafont $12.47
Keygos 4800mAh: Keygos 2/$17.99 - Use at own risk. Referred to as IMR protected, but description is Li-ion. Discharge test here, actual capacity only 2951mAh.
Hi-Max 4000mAh: ebay-pingyi.co.ltd 2/$27.50 - Samsung core.
If anyone is interested in learning more about Li-Ion battery chemistries (and if you use them you should), here are two excellent sources: