www.fabric.com is great and having a sale,
www.connectingthreads.com is also having a sale and then there is the all time favorite, Missouri Star Quilt. Also Fat Quarter is very good, but can be a bit pricey.
www.equilter.com is also having a sale, but I sometimes think their sales just brings them down to where most of the online folks are regularly. Connecting Threads is one of my favorites because they have some really good buys, their thread is great and they give terrific service. Have fun.,