Citer is a project under development at the Legal Information Institute (project details). It is intended to serve as an extensible resolver that will allow legal document references from one namespace (such as print citation, or that of a proprietary electronic publisher) to be resolved into the URI for an online resource. This can be done either by interactive, browser-based means (swipe-and-click, and perhaps someday via Ubiquity), or by submission of a raw text to be scanned for citations that are then linked.
The more research-oriented, speculative aspect of the project will go beyond detection of formal legal citations in the text to contemplate less formal references.
Citer will currently resolve references to the US Code, US Reports series (Supreme Court decisions), the Code of Federal Regulations, the Federal Register, and US Circuit Court decisions in F 2d. and F 3d.