For example, resources focused on etymological roots of words (e.g. Greek, Latin, etc), without learning those root languages entirely (not feasible), would be helpful.
For wrangling up new vocabulary, I'd prefer more than just a simplistic listing of words or thesaurus (most thesaruses suck, anway). Something more geared toward learning them. In addition to those, a decent (electronic and/or online if possible) thesaurus would be nice, noting that most suggest basic, obvious words (like the suck that is thesaurus.com).