(You can buy some of my work online at e23.)
To start with -- for systematic, if maybe erratically updated, overviews of my writing history, you might see RPG.Net or the Pen and Paper RPG database. But if you really want to know my record... Actually, I've been writing RPG stuff semi-professionally for longer than I care to think. Would you believe White Dwarf 20? Or a bunch of monsters in the original Fiend Folio? (Some of which have since reappeared in more recent D20-system monster books. With or without credit to me, in various cases. Not that I get bitter about such things, of course.)
Steve Jackson Games showed an interest in my work, and a book or two blossomed into a long-standing working relationship, which I've detailed in a whole separate page. (All the cover images were starting to swamp this one.)
Talking of Steve Jackson Games... I've contributed stuff to numerous RPG magazines over the years -- too numerous to list here. (These days, my short pieces make most of their occasional appearances in the electronic pages of Steve Jackson's admirable Pyramid.) And on the subject of periodicals, I'm vain enough to boast about having being invited to write material for the magnificent Dork Tower by John Kovalic. ("Clanbook Perky" and "Clanbook Mopey".) So I hereby do.
In the years that followed, I did a bit of work for Hogshead, a British company that used to have the license for Games Workshop's Warhammer RPG. This included a chapter and some editing on their first all-new scenario book, The Dying of the Light. (Note that Hogshead subsequently changed hands, and ended up publishing completely different games. For that matter, the Warhammer RPG is now being published by someone else, in a new edition.) Furthermore (and quite some time back now), I wrote a Champions scenario book called The Sands of Time, which, following a history too tortuous to be discussed before the eyes of servants or children, never got published. (That one seemed to be seriously jinxed. Sadly, these days, I think that its subject matter would make it difficult. I leave the cover art up for the morbid interest.)
At one stage, I also worked on White Wolf's Mage: the Sorcerers' Crusade line. For example, I wrote about half of Castles and Covenants. Somehow, the cabal rosters for the Order of Reason chantries that I contributed to that got lost in the shuffle -- so I've posted them on the 'Web. And then, for the same game, there was The Artisans' Handbook,of which I wrote the entirety. (Well, to be pedantic, a few paragraphs got added in editing. They usually do.) And the follow-up to that was The Swashbuckler's Handbook, by myself and Phil Brucato, of which I must admit to being immoderately proud. A couple of appendices got cut from that for reasons of length, so I've placed them on line, too. Unfortunately, the Sorcerers' Crusade line is now defunct.
Oh, and I've done some stuff for the wondrous Dying Earth RPG from Pelgrane Press -- specifically, about a third of Cugel's Compendium of Indispensable Advantages -- while the end of 2003 saw the publication of my first work for Atlas Games -- an Ars Magica adventure book named Faerie Stories, written in collaboration with Neil Taylor. My next contribution to that line took a few years, I'm afraid, but May 2009 saw the appearance of Tales of Mythic Europe, to which I contributed a chapter.
And I had a chapter in the late lamented Guardians of Order's Dreaming Cities. More recently, along with my continuing work for Steve Jackson Games, I contributed to Gatecrashing, a supplement for Posthuman Studios' Eclipse Phase RPG. This is available in electronic or printed form; if you opt for the former, you can buy either the book alone or the "hack pack" with added extras from DriveThrueRPG.