Government resources can be extremely helpful to your legal research. These materials cover anything put out by the government at any level-- be it federal, state, or local.
The plus side to free government materials is that they are often the most true version of free information found on the internet. The down side is the purpose of these materials is to push information out to the public not to impress the public. The lack of a marketing push, along with limited funding for these endeavors, can make the sites more cumbersome or less exhaustive than one might hope.
Another issue with government resources is the lack of continuity. Federal resources and state resources might offer widely different materials with very different interfaces. Even among states, or even among similar entities within a shared system (think different federal agencies) the variation can be extreme. This makes understanding what types of information might be available and where to find that information highly important.
Portal sites which link and organize government resources are the best place to start. Some portals are put together by a government organization and are themselves a government resources. In addition, third-party compilers and publishers also may produce government information portals.