My connection is suddenly very slow

I usually get 200-350 kilobytes per second download and 50 kilobytes per second upload, and for 2 days now I'm lucky if I can get 100K per second download. I checked my connections, they are all fine. I cleared my temp internet files and windows temp, no improvement. Defragged, no improvement. No viruses or spyware of any kind. What could be causing this probmlem? Is there some sort of online test that can see if the line is bad or if the internet in my area is bad? Any programs that do these sort of tests? Thanks for any help.