The Joy of Pitman Shorthand is a site covering some of the basics of shorthand. It's something of a work in progress.

The UK site Shorthand World has a decent collection of information, links, and products related to several shorthand systems, including Pitman, Teeline, and Gregg.

The Not So Complete Idiot's Guide to Alternative Handwriting and Shorthand Systems gives an insightful review of a number of different shorthand and handwriting systems, including Pitman, Gregg, and a Gregg-based system called Handywriting.

The Internet Archive has a large collection of shorthand-related documents, which you can find by searching with keywords like Pitman, shorthand, stenography, phonography. One caveat - most of the documents are quite old, and in some cases, they use letters or vowel placements that were present in versions of Pitman before 1857 (some of which persisted in the US) but were changed and improved in later versions.

Here are a couple of sample offerings:

The young reporter OR How to write short-hand : A Complete Phonographic Teacher BEING An Inductive Exposition OR Phonography, by Webster, Epinetus (1852). Or How to Be Decisive About Titling Your Book. This American book teaches an early version of Isaac Pitman's shorthand. (As noted above, the vowel placements and some of the consonants have changed since then.)

Which system of shorthand should we learn? by Enoch Barker was written in the early 1900s, and covers the various flavors of shorthand popular in the US at that time. The book (really not much more than an article) was published by Pitman & Sons, so, not surprisingly, the author has an Isaac Pitman bias, but it's still an interesting review of the differences between the numerous systems - many of them minor variations of Pitman - that were fighting for supremacy in the US. When this book was written, the competition was over in the British Empire - Pitman was by far the dominant system.

In the US, the battle between shorthand systems eventually boiled down to one between Pitman (in all its variations) and the newer, more unified Gregg System, which promised to do away with all the rules and exceptions in Pitman. (It does, but mainly by replacing them with a different set of rules and exceptions.) Gregg eventually became the dominant system in the US, and went through a series of variations, each progressively easier to learn... and slower to write with. This Gregg Shorthand site explains the Gregg system, and the differences between versions.