I heard this sentence in a song while playing Tony Hawks Pro Skater 2: "Eternity is a long long time my friend". This is very very true :). I totaly agree with whizkid except he doesn't go far enough.

Imagine all stars first turning to supernovae and then falling to black holes and just the matter fusion failing in the remaing stars.
Imagine all stars in the universe ceasing to exist. Not even a single photon will reach you. There is complete darkness and the temperature of everything will lie only slight above 0 Kelvin. The entropy will spread all matter in the whole universe until someday even protons and electrons won't exist simply because they are to old. I think physicians still don't know if the universe will spread forever or if it will collapse, depending on the Hubble Constant.
If it collapses you might eventually be saved from your eternal existance, if not, everything degenerates to complete silence and darkness. Forever. Perhaps you will experience the The Heat Death of the Universe though I think it should rather be called the Cold-Death.

Choose your religion wisely, or you might live forever.