Keeping on the "religion in government" front, a very technical tax decision arose in precisely that context. Arizona offers tax credits to parents for sending their children to private schools, including religious ones. A group of taxpayers sued, claiming that this might constitute an Establishment Clause violation (gee, where else did we hear that yesterday?). The parents sued only for prospective relief: they did not ask for revocation of past credits, but only that the court prevent future use of credits for religious schooling. The state claimed that this would implicate the Tax Injunction Act and therefore could not be heard in federal court. Under the TIA, federal courts may not hear suits concerning state collection of taxes. The Supreme Court upheld the Ninth Circuit's determination that the limited scope of the lawsuit took it outside of the TIA's restriction on federal jurisdiction. Objectively, this is the right decision. I've never been excessively fond of the TIA, because the reality is that state courts do not provide an adequate forum for challenging state taxing authorities. However much we have principles of federalism in our system of government, such an inherent conflict of interest must be outside the scope of such limitations. (And don't kid yourselves: It's not that the judges are necessarily "bad," although as elected officials in most states I'm not sure they qualify as "judges." It's that state procedural rules on tax matters stack the deck.) This might be most relevant to Los Angeles-area authors contesting the imposition of the "writers' tax."
Also on a very technical matter, the Court split the baby on international antitrust jurisdiction. This is the "vitamin pricefixing" case. The particular issue presented was whether US courts could use US law and regulate conduct outside the US that resulted in (pretty damned clear) antitrust violations outside of the US. The Court said "maybe." It rejected a theory that allowed for independent jurisdiction so long as there was some related conspiracy that otherwise fell inside US jurisdiction (harm to US consumers or actions by US actors). However, in a pretty strongly worded qualification of its remand, it stated that there might be dependent jurisdiction, if the facts of the particular scheme are so intertwined with clear US jurisdiction that the case could be heard here anyway. In other words, the scope and remedy for the conspiracy can consider purely foreign acts and effects, so long as they are inseparable from enough US-based acts and/or effects that the case could be heard here anyway. This is the right "prudential" decision; what I'm a bit surprised at is the decision's neglect of treaty obligations, which essentially demand this result.
Finally, there was an interesting discrimination opinion, but that's for another time.