The best place to ask this is probably candlepowerforums.com as they focus heavily on buying 18650s in low/moderate volume for their flashlights.
Just from some browsing of that site, if you are looking for protected cells, Orbtronic has a good reputation (although more expensive):
http://www.orbtronic.com/18650-batteries
People have also bought from fasttech (with better prices for raw cells):
http://www.fasttech.com/category/1420/batteries
However, avoid the cells with "Fire" in the brand name. They tend to be the cheap cells you are trying to avoid.
If you are buying a raw cell (without additional protection), look for the brand names: Panasonic, Samsung, LG, Sony, Sanyo.
Also, make sure the size is a good fit (some cells are taller esp. the "protected" ones, some are shorter), and that the charge/discharge current ratings are compatible with what you are replacing (you may have to look for datasheets on other websites). Some (like the Samsung ICR18650-30B) also have a higher 4.35V charging voltage and would have significantly lower capacity if charged to the standard 4.2V.
The best prices are typically on alibaba (sometimes ebay), but given the high probability of fakes there, you may not want to try that option unless you do a lot of research on the sellers.
