Best at form factor motherboard (revisited)

I have an old computer put together by myself without the motherboard
(or should I say - without a decently fast motherboard at least so far)
that I am looking for a motherboard for. It must be in the at form
factor because of the case and power supply and I would like a celeron
or socket 370 or socket a processor. I have a bunch of spare parts for
everything else. I have looked already and haven't found anything
worthy of considering and I am hoping I can find one of these
motherboards in a niche area of the market at the very least. Anyone
have any recommendations? I am not going the atx route because I would
have to replace the case, powersupply, memory about possibly more at
the very least just to get this system up and running. I like this big
at form factor case and can't find a cheap equivalent in the atx case
market (tried pricewatch/pricegrabber) and I can't see one reason
(except money) why the at form factor needs to be phased out. Quite
frankly the at form factor does NOT need to be phased out. Any feedback
anyone? Thanks!