Aside from getting angry on Prop. 8, or other discriminatory and obviously anti-gay laws, there are things that people might consider doing.
Here is my own personal list. Others may have different ideas.

- write letters to my US Senators, US House member, state legislators and governor, letting them know of my views and asking their views on specific gay related issues.

- contact organizations & charities that I donate to, and ask if they have a written non-discrimination policy. If they do not, or if it does not include sexual orientation, let them know that I will not continue to donate to them, until this is done. After all, it is my money that they are asking for.

- when making a purchase, especially a large purchase, go with the company that has a good rating on the corporate equality index. Is it perfect, no, but it is better than having no idea at all of the company you are giving your money to.

(see: http://www.hrc.org/issues/workplace/cei.htm)

- if at all possible, avoid giving any business to known to be anti-gay.
Exxon-Mobil scored 0, (so I do not buy gas from them). BP, Chevron, Shell all scored 100!

- Pick a gay rights organization, national or local, and support it.
A few options: HRC, GLAD, Freedom To Marry, ILGA
a much larger list can be found here:
http://en.wikipedia.org/wiki/List_of_gay-rights_organizations

- not be invisible (attend meetings & rallies and not be afraid to speak out when appropriate.