R is a tool for tackling large scale statistics problems, so if your math is rusty you'll want a refresher. Included in these lists are resources for a quick brush up & full courses to give you a firm foundation.
These books are useful to bring you up to speed on statistics as well as reference material as you're working through the application of statistics.
The Open Course Ware movement has prompted a rise in both the quality & number of free math & computer science courses. If you have the time to commit to regular study, these are all fantastic & highly recommended.
There are a handful of downloadable PDF e-books on statistics available. In most cases these are put together by university professors, but all are very high quality.