I'll take the risk that everything I suggest has already been said.
- a Rave. You can't have a nerdy convention without a rave. It's just wrong D:
- A decent dealer room.
- A decent Game room.
With some random TVs so people can bring their own consoles to the party too.
- Cosplay contest, with competent judges <3
- some random little events/shows/ect. Karaoke would be a good idea, and one con I went to had this thing called "Iron Cosplay" where they gave you scraps of fabric and stuff and told you to make a random costume of something specific (like an anime series, in my case, I got naruto), and you gotta make the costume in 3-5 minutes (or whatever short time limit).
- A music room, that has random music playing and maybe music videos. This is the room where Karaoke is usually held.
- previews of random games <3
- LAN party with a giant raid/excursion of some boss in some game. oh yeah.