Clustering techniques using R

Now that I've loaded a file into an R data.frame  and played with
linear regression until I got a good model, my next step is clustering
using the coefficients of the regression model (I have many files)
Thanks to some R experts'  guidelines I could find plenty of
documentation on regression analysis in the "contributed" section.
Some touch on the concepts of the underlying theory and then show some
worked out examples (extremely useful).
I found nothing so nicely explained and laid out about cluster analysis with R.
I would appreciate some suggestion about reading on techniques for
clustering using R. Some application examples are very welcome.
Thank you in advance for your help.

Best regards,
Maura E.

Maura E.M