"The American flag is a potent piece of national iconography, but its design shifted frequently until the early 1900s. What if it were redesigned today? " the Times
A quick browse through the interwebz (Wikipedia, no right wing bastion) found this (click on picture for larger version):
So since 1777 the only thing that has changed is the number of stars. I wonder why that changed? Hmm, might need to do some more research.
Here's the link to the original.
After writing this it occurred to me that readers who depend on the Times for their information might not know the actual history. So here's a quick note for you. The United States Constitution was officially ratified by sufficient states to go into effect in 1788, so the only flag we've ever had predates the actual Constitutional Republic by 11 years. Just saying.