I've been playing flute for a while now and I've been striving for great tone but I feel like I've hit a wall. I try to make the best tone I can but I don't know what to strive for. I play notes in the high register and they sound crass, does that mean I'm making a mistake, or is that just the nature of the high register? If I had an example of good tone I would know just how far I can go. So far the best I have is this website http://andrewhugill.com/manuals/flute/rangeflpp.html. If there was a resource you had that I could you to see how good my tone is I would be grateful.
You didn't specify how long you've been playing. Is "a while" a week? A month? A year? Great flute tone does not happen overnight. Great tone is based upon building the right foundation on fundamentals. Have you studied with a private instructor who can see and hear you and advise you where your weaknesses are? You can only teach yourself up to a point and then you need a tutor to help guide you over the humps.
Great tone requires building a good foundation of breath support, lip flexibility, and lip strength. Anyone can run, but to run a marathon requires training to build the leg muscles, lung capacity, etc. Playing a flute is no different. You have to build the PROPER foundation.
The best thing to improve flute tone is to practice playing long tones for at least 15-30 minutes per day. Jennifer Cluff maintains a website with lots of good information about improving your playing. Here are some links to her pages about improving tone, playing long tones, and high note warmups: