You are correct, there are an enormous number of choices.
Could you help us to help you, by adding a few parameters ?
Budget ? (even a range is very helpul)
Size ? (yes, keychains vary a lot in size)
Output ? (single mode, multi-mode)
Preferred battery ?
Format ? (flat, round, built-in cell, replaceable cell, built-in charger, etc)
Material ? (plastic, metal, aluminum, steel, titanium, exotic / other)