I received a few off-list responses to my question about GUI interfaces for R, so I thought I’d repost everything for other interested parties.
The two recommendations I received that look most promising were R Commander and R Studio. Also recommended were the Quick-R website, as well as the books R in Action, R in a Nutshell and R for SAS and SPSS Users. Also suggested was the O’Reilly catalog of R-related books. I got a bit of info from the Revolution Analytics site, as well as some helpful course materials from Trent Buskirk at Saint Louis University.
Thanks again to everyone who responded. Looks like I have plenty of reading ahead!