[elhigh]

For the cheapest heads-up instrumentation option, you can purchase the Torque app (I don't know if it's available for iPhone, probably is) and get an OBDII adapter to send to the phone. NOTE: be certain you get a WiFi-capable adapter as I understand iPhones don't do Bluetooth.

Don't forget to check your tire pressure. Even if you're not willing to push them all the way to the upper limit specified on the sidewall, you can still ascertain that they're at least as high as they're supposed to be. That made a huge difference on my Civic.