Ideas for minor hp mods?

I was talkin to some friends today about makin some minor mods to my car to get it slightly faster than stock, (and maybe hide it from my dad until I go to college) and we were talkin about maybe just buyin a K&N air filter to replace the stock with, anyone know how much hp it gives or if its worth it?
Was also thinkin maybe get a programmer and was curious what y'all thought of as far as companies for the programmers, figured i could use it when i was drivin then default it back to factory settings when im not (incase dad uses it) and wondered how much hp those usually give.. any other ideas would be good
thanks ahead atime,
Wes