Although all you need to take good photos is a camera, there are some accessories that can help at times.
Bigger Memory Card
Most cameras ship with small memory cards, and you may feel as though you should shoot at a lower resolution to save space. Don't do itjust buy a larger memory card. Visit www.dealram.com to compare prices at multiple vendors for the type of memory card your camera uses.
USB Card/PC Card Reader
If you have friends with digital cameras, a USB or FireWire (much faster) card reader that accepts all the types of memory cards can make it easy to share photos of an event on the spot, without having to mail them around later. Folks with PowerBooks might also look for a PC Card adapter that lets you plug your memory card right into the laptop.
Also consider an iPod with an attachment like Apple's iPod Camera Connector, the Belkin Digital Camera Link, or the Belkin Media Reader; they let you offload photos from your camera to your iPod. Search for "iPod camera" in Google to learn more.
In low-light situations, if you don't use the flash, you risk your photos coming out blurry. The solution? Attach the camera (most have the appropriate threaded mount) to a monopod or a tripod. Documentary photographers are less likely to want to use even a monopod (which is smaller and faster to use than a tripod) because of it getting in the way, whereas artistic photographers are more likely to accept a little extra annoyance in exchange for the highest quality photos. Either way, make sure it's easy to use.
It's unfortunately common to run out of power at a bad moment, particularly if you're using your camera's flash or LCD display a lot. Avoid missing great photos because your camera is dead by carrying an extra battery pack or set of batteries. Proprietary battery packs tend to be expensive, but my experience is that it's worth buying the camera vendor's battery rather than one from an independent manufacturer. Other cameras take standard AA batteries; you can use any normal battery, but it's cheaper and more environmentally friendly to use rechargeable batteries, such as those available from Quest Batteries; visit www.questbatteries.com.
Lens Cleaning Kit
Those of us who have used only digital cameras may not realize that it's well worth getting a special lens cleaning kit that can remove dust and dirt from your lens and LCD (and for cameras with removable lenses, the CCD inside). Normal cloth might cause scratches. Any camera store should be able to recommend a lens cleaning kit.
With iPhoto, you can always order prints from Apple. But you may want to print them yourself, perhaps for instant gratification, greater control, or privacy reasons. For that you'll need a color printer. There are a number of different technologies, such as inkjet, laser, and dye-sublimation. Inkjet printers are the most common (buy a six-color printer for the best photo quality) and offer excellent quality, but have high per-print materials costs. Dye-sublimation printers have the best quality for photos, but are more expensive. And color laser printers are the cheapest to run for many prints. You can learn more at camera review sites, which also often review printers.