If you are interested in security there are at least two or three good conferences happening every month somewhere. Some are listed below. BlackHat (big and expensive), Defcon and various Security BSides are always worth attending. There are some great ones in South America (H2HC, YSTS, ekoparty) and of course there are a lot in Europe (Chaos Communication Congress in Germany, HITB in Netherlands, NoSuchCon in France).