What is a good flash to buy for sony a100? for new user?

For sports pics, I would (and did) splurge and get the Minolta 5600 HS or the Sony equivalent. This is an expensive flash, but I did not regret the investment. It produces more light at a greater distance than anything else you can buy. And it comes with a full complement of features that all work with the A100: wireless remote flash, full angle and tilt head, AF helper lights work, turns on the camera's HS feature so you can shoot at any shutter speed, etc. I first got this flash to use with my Minolta Maxxum 5 film camera for shooting soccer pics. I later used it successfully with my Z3-- first foray into digital. When I went to upgrade to DSLR, the ability to use this flash was a big deciding factor in going for the A100 vs. other camera brands. About this time of year, the high school players that start games at 7PM are finishing play under the stadium lights. I found that I could stand on the sidelines and illuminate a player out in the middle of the field with good quality results. That's about 40 feet away. Fantastic. The flash/camera combo are smart enough to limit the flash's light output based on distance, ambient light, etc. In lower light output situations the flash will recharge almost instantly But in a situation where you are pumping out all the light you can, recharge will take several seconds, depending on the condition of the batteries. Bring fresh spares! The 3600 is a good flash too, but you will not get some of the features of the 5600, and you will not get the light output of the 5600. Spend the extra hundred bucks and get the 5600 so you are not wishing you did later.