[R] favorite useful tools?

[Carl Witthoft]

Hi,
I'm relatively new to R, so I don't know the full list of base (or 
popular add-on packages)  functions and tools available.  For example, I 
tripped across mention of rle() in a message about some other problem. 
rle() turned out to be a handy shortcut to splitting some of my data by 
magnitude (vaguely like a sequence-based histogram).
So I thought I'd ask: what small, or obscure, tools and functions in R 
do you find handy or 'cool' to use in your work?

Thanks
Carl