Hela live cell confocal laser scanning - reccommendations for good fluorophore that will show good movement
MitoSOX looks pretty cool. I've never used it myself, but I'm sure you could see some cool mitochondrial dynamics going on. Its a bit pricey though, but all dyes are going to be.

Even at only 8 hours you should probably be able to see a few divisions, which would be cool with hoechst.