Next time you get pressured to buy extras like TV, S-video, audio, Ethernet, USB or firewire cables, tell them you're going to Monoprice.com, where you can get all of them for under $5 a pop. The site also has tons of converters, adapters, and even HDMI switches (Gizmodo) for a fraction of what you'd pay in a retail store. Monoprice also stocks cheap car charger accessories and USB hubs. The site doesn't explain much, though, so it's best to know what you're looking for going in.
(Image courtesy troutcolour)