Ultrasonic sensors

I'm building a couple small robots and would like to use ultrasonic sensors to detect obstacles. I have a Ping sensor from Parallax that I'm trying out, and it works ok, but it requires code to work (send pulse, then measure time of return pulse in a loop to calculate distance). I would really like something less code-timing dependent, perhaps a voltage I can read with an analog input. What sensors have you used, and how "independent" are they?

The Maxbotics sensors are cheap and are fully automated.
PWM, Analog and Serial out and you just read it when you want to for Analog.

You can also use the pulseIn() function to read the response from the Ping sensor. It handles the time dependent code for you, and gives you microseconds.

Cheater - I've read about the Maxbotics sensor and it sounds great, have you tried it?
Mellis - Thanks for pointing that out! That's what I need to do for my Ping all right. I think I'll get another Ping for my first bot and try a pair of Maxbotics sensors on my second one.