Something like this

http://mycarprojects.net/fuel_share.aspx?car=224
Here are screen shots if you don't feel like clicking the link.

 

i guess is pretty good. but i dont see my self keep tracking with that.

 

I am going to write a php+ajax page to do that.

 

not online... but ever since i got my STi in 2003 and my 4runner since mid 90s, i've kept an excel spreadsheet...

 

I just use a program on my iPhone called MPG. I just type in what my odometer says when I'm going to fill up, input how much my tank cost for that fill and it will automatically tell me how much my gas mileage was and the current gas price was. It also keeps it in order by date of fill.

Basically just like this site but on my phone.

 

I keep a notebook in my glovebox. Every time I get gas, I input the date, mileage, gallons, and price. I also enter "life events" for my car like oil changes, new mods, maintenance, etc. and the corresponding mileage.
A friend of mine saw me making a refueling entry, and she called me ****

 

I don't write it down, but I average like 24-26mpg on my car. Not too bad I guess.

 

I think I've seen and tried that one on my iPhone. I usually use the mobile version of the above site or write everthing in the notes progam to input later

 

I thought about doing the same but suck w/ PHP

 

Yeah, I went from getting like 17 - 18mpg to almost 22mpg in my WRX. Driving slow FTW!

 

i just calculate it when i fill up and write the mileage on the back of the receipt.