I normally stick a film or DVD on, that way I'm sat at my desk, and seeing as I've just started watching *insert film/series of choice* I may as well carry on painting until the end. My favourite to work like this too is
SG-1, I've seen them all so many times I can tell whats going on just by the script and sound effects. Another good thing I've found to do is keep a couple of random models around that require a totally different approach to paint. That way if I get bored from , in my case, painting yellow all the time I can switch to something different and refreshing. And failing that take the current project to the gaming table. Nothing like seeing those half painted units perform well to get the drive to finish them!