Shiny Gold was the first.
Off topic-ish rant:
I remember playing FireRed and R/S/E, then wondering if there was a GBA version of Jhoto (at the time, the NDS system had come out pretty recently). I Googled and searched, until I stumbled upon Shiny Gold (it was a GBA file not an IPS in case people were wondering). After playing it, I learned that it was a hack! I tried to then find more hacks which I could play and wound up here (back in I think 2007-ish). I made an account to download hacks and such (which is what I did lol)..
I have long since forgotten the username, password and email for that account, but recently I decided to start hacking myself (started about early November-ish last year). I played a couple of hacks again out of sheer boredom. I think they were Sienna, Genesis and Rujin adventures (if that's how you spell it?). In my time, I've played a lot of hacks, and kept my eye on some of the better ones (which have long since died off :P).