Check out these results from webpagetest.org:
Looks like something is holding up the first response. That looks like the major issue, hopefully it's not too hard to figure out. I'm thinking maybe either the server needs to be kept alive, the databases are fragmented like Darrin said, or there is a problem with the communication between the web server and the database.
Along with some of the previous suggestions, it looks like you could benefit from using a script manager
to reduce the number of script files being called and you should compress your images for the web