These are just a few I looked around for, they'd probably have real immediate effects:
The Inventory, by MajinDragon
PVP suggestion that's very simple, by Cubical
Fortune Box, by Seeya
Stat Changes/Updates, by MajinDragon
Another idea is to expand the current maximum stats, of 30, to a number which would allow for more varied stat combinations on items and thus, more room for new items to move into. The benefits to current stats would need to be scaled properly with the new max so that we obviously don't get people walking around with inf weight cap or too much hp/sp/grace. The real victory would come with people never being able to get 100/100/100 (str/dex/con) but instead something like 95/89/97 or 90/93/95.