Does what it say on the tin 

http://distancetomars.com/

Add another 300,000,000km (186,000,000miles) for being at the furthest point. The distance they're estimating in pixels is about 55,000,000km.
How about an app that shows the current distance to Mars?

Found one in miles...

Mars distance calculator.

While Freddy's link provides a little bit of interesting information, and contains a moderately cool effect, I probably wouldn't visit it again, and if not for said interesting info, would have to vote for it for "most boring website". Sorry, Mate, but there it is. Plus, it didn't flash past the Sun, as Mars is near opposition right now.

Still, good information, so

I never said it was exciting