One thing I forgot to mention when it comes to "meaningful." If there is a company that actively gave to same-sex marriage ban campaigns or has a known record of discrimination against Gay, Lesbian, Transgendered or Bisexual people, then write a letter to them expressing your views, and don't patronize their business or buy their products until they change. Hit them in the wallet where it hurts.
In other news, I am dismayed to read some of Prince's views on gay people and same-sex marriage. Yes I get it that it is part of his beliefs, and he can choose to believe them and express those beliefs. At the same time, I can choose to basically say "I think your narrow viewpoint stinks" and not buy any more of his music. I have dropped his music out of my active rotation of MP3's, removed Purple Rain from my Netflix queue, and like I just mentioned, I won't be buying any more of his music.
Too bad, he's a talented person, but he doesn't deserve my money.