Fbootstrapp is an awesome toolkit designed to kickstart development of iframe Facebook apps in both relevant sizes. Based on Twitter’s great bootstrap, and coming with some LESS goodness (like Twitter’s bootstrap), this iframe Facebook apps creating toolkit includes base CSS and HTML for typography, forms, buttons, tables, grids, navigation and many more.
Also, the awesomeness of this iframe Facebook apps creative toolkit is that it provides styles similar to Facebook to make the user more comfy using your application. Also, included in the creative toolkit is a 520px grid perfectly suited for creating fanpage tabs. Aditionally there is an 760px grid suitable for bigger standalone applications (canvas is also included).
On the page, every element from the iframe Facebook apps creative toolkit is well explained to let you control the bootstrap better. Every element is explained with examples to make your life easier.