If you drive your car in winter don't even wait to buy synthetic. It is unbelievable how much easier the car will start and you can tell the motor is not so loaded while warming-up when it's 15 degrees. I'm still blown away how easy it starts when it is 20 below.

As for changes- I use Mobil1 and Wix filters. DO NOT BUY FRAM FILTERS! (they are cardboard inside!) Use Acura, Wix or Purolator. Anyway, I change my oil at 10,000 miles with a filter change every 5,000 miles. When I pull the cam cover the head is just as shiny as the day I bought it and I've had an oil anaylsis done and it came back excellent.

Farmers swear by Archer synthetics- supposedly they will 'hint' you can change your oil every 15-20k miles. I wouldn't wait that long, but if the oil is that good it's still better.