My favorite thought is that they've sent probes millions of years ago and we could send a request to watch some HD surveillance of dinosaurs roaming the Earth. It'll just take ~3k years to receive the requested footage.
Assuming an acceleration of 10 m/s^2 (similar to Earth's gravity), it will takes roughly one year to accelerate to a speed close to the speed of light were relativistic effects occurs, and you will need one more year to decelerate.