If memory serves, I used to use a program called QuickSFV for the purpose. Worked okay. It has been a while, so I'm not 100% sure it was that.

However, I came to find separate .sfv files a nuisance. All fansubbers include the crc32 in the file name and I can't say an extra file would be all too optimal, especially if you happened to move individual files, not always the whole directory containing the .sfv. So, I coded my own program that calculates a file's crc32, checks if the file name contains a string that looks like a crc32, and if it does, it checks if the freshly calculated one is the same as the one in the file name. If it matches, everything's alright. If it's a mismatch, the programs tells you so and gives an option to replace the old crc32 with the new. If there's no crc32 in the file name (like for example Horriblesubs' releases) the program can add it automatically to the end of the file name. As an added bonus the program allows you to replace spaces with underscores (or whatever symbol of your choosing), so that all files in the directory look similar. You can also force a renaming for the same purpose, as by default it won't rename files with a correct crc32. You can also set the type of symbols the crc32 is contained within, such as the default square brackets. The program allows a regular open file dialog or simply drag and drop, including a whole directory (although it doesn't support recursion, so directories within directories aren't scanned infinitely). Renaming requires a separate button click, so you don't rename anything by mistake but can check the preview list first, deselecting or selecting individual files if necessary.

Uh, that's enough of boasting, I suppose.