These days, everything wants to hook up with your iPod
There have been so many peripherals designed just for the iPod. Most are made by third party companies licensed to create products especially for the iPod. Some third party iPod peripherals aren't officially sanctioned by Apple at all and will often use a not so vague euphemism for iPod on their packaging. Despite what Apple might tell you, this is not necessarily indicative of a bad product, but as always buyer beware.
If a protective case says it's designed for an MP3 player, and shows a picture on the box of someone loading a device that looks much like an iPod, be sure and read the fine print. Was it designed for the iPod? Will it fit your iPod? These are questions you must answer before making the purchase. This can be easily settled with a money back guarantee- if you're not satisfied with any iPod peripheral you've just purchased. But the lack of official sanctioning from Apple alone should not deter you from purchasing a product. You may find that for the more generic items not using Apple's proprietary technologies, such as a carrying case or headphones, you might save some money on the item.
Non-sanctioned items aren't allowed to use proprietary technologies, like the iPod's docking port. However, the third party could produce an item that works for any MP3 player that utilizes the headphone jack. But remember, unless you're plugging headphones into your headphone jack, chances are whatever job you're hoping to accomplish with the peripheral device is better served using the line out from the iPod's docking port.
Most of the iPod peripherals are made by officially licensed companies who use Apple's technologies. Some of the support hardware you may find will even come from Apple. When shopping for iPod peripherals, there is a lot you have to watch out for when too many companies are making peripheral support hardware that is supposedly for your iPod. There are choices to make and often compromises too.
Cost is not necessarily proportionate to the quality of any device and this is especially true for iPod peripherals. Monster, for instance, makes good quality analog audio cables. Monster has a headphone to RCA output jack that connects to your headphone jack and provides you with high current RCA cables to connect to any home or car audio device with RCA ins. The trouble with this approach is that the current from the headphone jack is very limited and the Monster product is one that will cost you top dollar.
A much better option is any RCA output that uses the iPods docking port as it can provide you with a flat, clean signal to the RCA jacks. There are less expensive line out to RCA cable adaptors for the iPod than Monster's offering and they will surely provide better quality sound to your outboard amplifier.
Here is a rundown of various iPod peripherals. While not the only options available to you, these should help you narrow down your choices and hopefully make you a slightly more educated consumer when you shop for your iPod.