Depends on what you want to transfer between the iPhone and iPad. There are good solutions for some things, like pictures using PhotoSync; others are better served by using a cloud service like DropBox or Box.
Almost all iStore content can be downloaded to any device you own, as long as they use the same Apple ID for the iTunes Store. You can even set it up to happen automatcially under settings for the iTunes and App Store.
Thre is no way, that I know of, to just generically connect two devices so that they can see everything on the other device.