Light Platinum's a good hack to playthrough. Crazy graphics, plenty of 'mons, though the writing isn't the best.
If you like adult humor (not talking porn or anything), then Pokemon Clover might be up your alley. It's a complete hack in just about every single way imaginable, from new pokemon, to new music, and some great areas to run around and explore. It also has some of the most hilarious writing I've seen in a hack.
Pokemon Shiny Gold Sigma is flat out awesome. Not sure how up to date it is on RHDN's database, but currently there's pretty much EVERY POKEMON EVER in it. Starts off being a jacked out remake of G/S/C with extra things to do all over the place. Again, not sure how up to date it is in this site's database, but an update scheduled for November 9th adds in the Hoenn region, on top of the Johto, Kanto, AND Orange Islands regions that are already there. Just don't play it on PSP - it's GBA emulator can't handle it Everything else seems to run it great.