The Canon rectangular hood for the 50/1.8 is probably the nicest one to use. Cheaper than the "correct" round Canon hood, and easier to find. (Also, the correct round one is quite large, blocks a lot of finder.) Very nicely vented for viewing.
I presume tha the 50/1.9 rectangular hood that rover pointed you at will work fine as well. I've never tried that combination. It's narrower and deeper.