The American Community Survey is created from a large sample survey and is updated on an annual basis. As far as the Census datasets go, it is the most comprehensive (in terms of subjects) and geographically detailed dataset that is published on an annual basis - it will probably be your first choice.
One alternative is the Population Estimates Program. It's also published on an annual basis, but it only includes basic variables like age, gender, and race, and only for large areas like states, counties, metro areas, and places (i.e. cities). It's simpler to work with since it's smaller and isn't sample-based (data are estimates computed from births, deaths, and migration). If you just need the basics for large areas, it's a good option.