Buy a good cable. Note that good doesn't mean expensive. Whatever you do, don't buy from a Big Box retailer (BB, CC, etc.) and the like. Retail stores charge way too much. Buy from Amazon or other online suppliers. My personal favorite that I used for my home theater projection system is Blue Jeans Cable (google them) - they have good quality cables for reasonable prices. Their Tartan brand is very economical if you don't have a large budget. Avoid 'M@n$tur' they are overpriced and not any better than any other brand (don't buy into the hype!)

For short runs of less than 3 feet you can probably buy the cheapest $4.99 cable you can find. For longer runs (over 10 feet) get a better quality cable as otherwise you may get signal degradation. I have a 35 foot cable that I purchased from Blue Jeans and paid around $99. The same length of cable in a retail (big-box) would probably cost my three times that amount - assuming I could even find one that long. And BJ's quality is so good, I don't need an amplifier or booster on the cable.

As for hooking up to your TV. HDMI will transmit sound to your TV, but note in most cases you will only get plain old stereo. If you want Dolby Surround that is supported on many games, you need to either plug your HDMI cable into a capable A/V receiver that accepts Dolby over HDMI (most will) or you need to have a separate digital optical cable plugged into your receiver. This is because most TV's only have small left and right speakers and lack the processing equipment to process Dolby Digital. That is why a separate A/V receiver is needed to get surround sound. Of course, if you don't care about surround sound, then yes, the HDMI will pass plain old stereo 2.0 to your TV. Home Theater forums are good sources of info on cable because HT often places higher demands on these cables than most PS3 users will.

Make sure you enable your sound output on the PS3 to either 'HDMI' or 'Optical', or whichever connection you end up using. Note: that with the PS3 it will only pass sound through a single source at a time. So if you have your TV connected and a receiver connected optically, you won't hear sound through the TV and the receiver at the same time. You have to choose where you want your sound directed to. This is how I have mine setup: HDMI to TV, and Optical to an older non-HDMI receiver. I have to turn on the reciever to get sound - but it's in surround which is way cool.

I hope this helps.