Best way to test an Arduino sketch without uploading to the board?

Hi
What do you think is the best way to test an Arduino sketch without uploading to the board?
ie. What is the best piece of software available?

I'm currently writing an Arduino sketch and it would be very usefull if I could test it without having to upload it to the actual Arduino board, particularly because I'm writing the sketch at home and I only have Access to the Arduino board once a week.
I've seen a few solutions out there but they all seem to complicated for me (a very beginner in Arduino coding), so which software would you recommend?
It would be useful if I could change the inputs in real time and observe the outputs from the pins.
Thank you!

Have you tried any of the many results Google gives?

I was looking into this same question about a week ago - although I've not tried any, these looks to be the most popular and discussed:

http://www.arduino.com.au/Simulator-for-Arduino.php
http://www.arduinodev.com/arduino-simulator/
http://www.virtualbreadboard.com/

Would be interested to know what the outcome is if you try any.

Here's a list of ones we have identified:

"http://arduinotronics.blogspot.com/2012/11/arduino-simulators.html(arduino simulators)":http://arduinotronics.blogspot.com/2012/11/arduino-simulators.html

Thanks, I tried these and a few from the link given by Steve Spence, and
http://www.arduino.com.au/Simulator-for-Arduino.php
was by far the best. There is an annoying 30 second free version delay every time you update the sketch but apart from that its perfect for me.
Cheers guys.

Excellent - thanks for letting us know! If you get any time, it would be interesting to know what pros and cons there were of the others.