If you want practicality, nothing. I would, instead, save my money for other stuff such as upgrades. Attachments are nice if you want aesthetics, but your guns' irons work just as well for your effective range as any reflex sight. (again, this is my own opinion)
If you want aesthetics though, you could get an Eotech replica. They're a bit pricy but hey look gorgeous. You could also stick a laser pointer on it if you want for hip shooting at close ranges. I have a foregrip, but as steyraug said, not everyone likes them.