I've found a bunch of iPhone objects inside interface builder, but I assumed there would be a standard pack of icons, gradients etc to make things more applelike.
How should I create these graphics, simply using pngs or are there special drawing tools shapes I can use inside interface builder?
You can use any type of images supported by iPhone SDK natively. Here you will find a list. But. for your convenience I will also list it here:
Hope it helps.
No, you won't find any shape tools in interface builder itself.
You might search around in the developer connection, for example: https://developer.apple.com/iphone/library/samplecode/UICatalog/ has some image files with apple-like buttons. These can be programmatically "stretched" to any size, check out [UIImage stretchableImageWithLeftCapWidth: topCapHeight:]
Some images, such as those appearing in a tab controller (see along the bottom of the screen in the world clock app), are stylized for you. You provide the image, e.g. just the alpha channel of the shape and it automatically gets the blue gradient when it's selected.
Also, .pngs are supposedly optimized by XCode for use on the iPhone so despite the plethora of formats it can support, you might stick to .png