Evan found a great tool for quickly testing your site to see how it looks on a few common mobile platforms. Just enter your site’s address in the upper right and see how it looks.
http://jamus.co.uk/demos/rwd-demonstrations/
BTW: We have seen a huge increase in request for building out responsive design recently. If you need any help or have any thoughts just email us (info@switchboxinc.com). We are always looking for good development resources so feel free to share your thoughts or favorite web tools.