I really like Superior Thread's "So Fine." It's thinner, so it blends in and you can't see my oops's.
I've learned that Coat's and Clark's is an expensive thread when you price it by the yard. It's less expensive by the spool, but they don't put much thread on the spool.
I've heard good things about Wawak, but haven't tried it.
Maxilock actually works well for machine quilting, and is pretty inexpensive. I was skeptical at first about using a serger thread, but I learned that Kathy of Kathy Quilts uses it more than other threads.