Whether you plan on upgrading to one of the new iPhones or iPods announced tomorrow, or you already have a device with a Lightning cable, you don't necessarily have to buy a new dock. Flybridge created a little adaptor that turns your old iPod 30-pin dock into a Lightning-compatible one.
Simply take your existing 30-pin dock and Lightning adaptor, connect them, then slide on the Flybridge adaptor. This will make your dock actually hold your iPhone up rather than connect it with a lot of potential wobbling. While this solution could be cheaper, the Flybridge adaptor saves you from buying an entirely new dock.
Flybridge Dock Adaptor ($15) [Flybridge]