I like the LiftLaws site a lot and they do appear to make a good effort to keep up to date.
HOWEVER, keep in mind that they may not catch everything. Searching the law of all 50 states and keeping on top of subsequent developments is no small feat.
What I like about the site is they point you to the statutory and administrative code provisions upon which they are basing their conclusions. With the help of Google, this means you can then usually find the original provisions for free online at your particular state's website quite easily. Depending on your issue, you may want to use this method to follow up and double check LiftLaws' conclusions.
For example, JK'n and I recently discovered (through a long, exhausting, and sometimes heated discussion . . .) that LiftLaws' opinion that there are no restrictions as to wheel spacers in Massachusetts is only potentially correct. At best, the actual code provisions are ambiguous on the topic, and there is an argument to be made that they are in fact unlawful.