If you are interested in trilobites, that most successful and fascinating class of Palaeozoic arthropod, I heartily recommend visiting Sam Gon's website:

Trilobites - well-worth keeping an eye on.

And if you're looking for a really excellent guide to the group, click on the link on the front page and shell out a measly $6 (£3.95) to download Sam's pdf.  With clear diagrams, wonderful pictures, and fascinating text, you won't be disappointed.