What tools are available for EEG analysis on the R platform? I'm starting some EEG studies on attention, and would really like to use R for preprocessing (filtering/artifact rejection), visualization, and analysis, but I can find very little in the way of tools. If there isn't a standalone package, what packages might be useful? 

Things I want to do:


Condition categorization according to events, and comparing all subsequent analyses by condition
Power spectral density in specific frequency bands (SMR, theta, beta, alpha, etc.)
Event-related potentials
LORETA (low-resolution electromagnetic tomography)
Antoine Tremblay has just released an advanced analysis toolbox: http://onlinelibrary.wiley.com/doi/10.1111/psyp.12299/abstract

It's missing about half the features on your list, although fundamentally, spectral density is a simple task and LORETA is a stand-alone package anyways (although similar approaches, e.g. general CSD estimation, are implemented in many packages). Basically, once you got the EEG data read into R and cleaned of artifacts, ERPs (simple averaging) and spectra are fairly basic tasks and LORETA is an external toolbox agnostic of where it's getting its data from.

Alternatively, I would propose to use either one of the two standard MATLAB-based solutions (EEGLAB or Fieldtrip), or MNE in one of its iterations (e.g. the one in Python). All of these will handle the tasks you're talking about.