I agree with the ignoring advice. Works for me. If it isn't a full blown tantrum, I just tell them to sit in the crying chair until they are finished, then go about my business.
Funny true story: Mom said that I started throwing some pretty massive tantrums about 2. One day, she picked me up and tanned my britches (it was nearly 60 years ago, she was allowed).
According to her, the next time I threw myself in the floor to have a tantrum, I sat there a minute then sighed and said, "It's just not worth it," got up and went about my day. She said it didn't stop tantrums, but they were never as frequent or long after that.
