pv is a great tool. One of it's lesser known features is throttling; transfer a file without dominating your bandwidth: pv -L 200K bigfile.iso' Complete with a progress bar, speed, and ETA.
Similarly, though useful less often these days, using -B/--buffer-size to increase the amount that it can buffer. If reading data from traditional hard drives, piping that data through some process, and writing the result back to the same drives, this option can increase throughput significantly by reducing head movements. It can help on other storage systems too, but usually not so much so.