So my husband has worked his butt off doing overtime which means he is going to buy me a present

I am thinking a flash and I have no idea which one would be good for me. I think I would want it primarily for low light indoor photos of the kids bouncing it off roof, walls etc but I would also like to try using it for cycling photography...where do I start?? Do I need a Pentax or is another brand eg. Sigma, just as good??