The last family pic that we did, about a month ago, my husband wore a blue, black, red, and white striped shirt. My oldest son wore a black, white and grey striped shirt, my 2 year old wore a red polo shirt, and I wore a blue polo shirt. That way we were still coordinated, but not trying too hard. The pictures turned out really great. We did a big family picture w/the in-laws and all to where we all wore either black, white, grey, or red shirts. Those were taken outside and just looked really pulled together.
I am also a really big fan of the jeans and white long sleeved dress shirts for the whole family, but leave them untucked! I think going without shoes and just really comfortable make them look a lot less posed too.