I recommend the following cell brands for use in flashlights.
1. AWs Protected Li-Ions, available in many sizes... they are available at Lighthound and through his sales thread in the dealer section of this forum.
2. Wolf-Eyes Protected Li-Ions, available from Pacific Tactical Solutions
3. Pila Protected Li-Ions, available from Jsburlys
These are the most commonly used because they are the best quality cells available, and they have protection circuits that make them safer than ordinary "bare" lithium-Ion cells. These 3 brands of protected cells are the only protected cells on the market with high current thresholds set on those protection circuits, this is done specifically with the intention of being able to light up powerful incandescent bulbs. I do not recommend unprotected cells, or any cells that claim to be protected from other sources.. Going on ebay and picking up some really cheap cells is asking for trouble. Do so at your own risk, and understand that they may not work in your configuration.