I like Ali's answer in the context of the 4yo.
However, an 8yo is greatly different. An 8yo has a much broader understanding of the world, social expectations and contracts placed upon them, and should understand specific definitions of Right and Wrong. A 4yo barely understands that other people can have ownership of things, too. An 8yo can understand the lesson in Cars (basic respect towards other people) that isn't explicitly spelled out in skywriting.
If you're talking abotu an 8yo that told a 1-off lie about something that could really get them into hot water, then I would suggest dealing with the fact that they lied and move on. Ali's list above would work well, I think.
However, an 8yo that lies regularly is a problem beyond in/consequence. even inconsequential lies are consequential at that point. I would recommend going back to the drawing board and attempting to establish what the real problem is and whether or not they understand socially Right and Wrong. Either way, it's probably time to seek a professional.
Appropriate discipline? Man, you know your kids better than I do. What has worked for me with all 5 of my kids is spanking. The only time they get the hand is if they lie. Consequently it rarely happens. 1x a year maybe... matter of fact, i don't think i had to spank the 8 at all in 2011.
But again: your kids. What works for me may (probably) not work for you.