A great way to save bandwidth on your website is to make sure compress your PNG images to reduce their size. There are a lot of special utilities out there that do this in such a way that you get a great reduction in file size of your PNG without losing any noticeable image quality. Probably the best know of this is PNGCrush.

But if you're one a Mac, you don't need special software for this, you already have a great PNG compression app on your computer: Preview! That's right, preview! Open any PNG file (or a whole directory of them) in Preview and then select "Save As..." from the File menu. Preview will save the file and it'll be a *lot* smaller afterward. I compared Preview to PNGCrush. PNGCrush was slightly better at saving space, but Preview is so much easier to use that it's now my preferred tool for reducing the size of PNG images.