Ah, another one of these... :-) If you search for online fabric shops on this board, you'll find several threads posted in the last few months alone.
I've ordered from:
webfabrics.com
thousandsofbolts.com
favoritefabrics.com
equilter.com
fabric.com
So far I've had good experiences, I'd happily buy again from each of them. Fabric.com are a bit odd for international shipping, unlike most they won't split your order if sending it in two envelopes would be cheaper than in one big box so I have to watch out what I'm doing with them.