Alienware are good machines - quality components - but you'e throwing away $500-$1000 to have them put those parts into one of their l33t cases.
If you just want a silly case, there is a good selection if independent manufacturers now: try
http://www.xoxide.com/allcases.html
Dell can give you an ok low-budget machine, but their higher-end desktops are a total ripoff. (laptops excluded)