I'm only learning myself. But as far as I know, when simply making straightforward future tense statement 겠어요 is ONLY used when talking about yourself. The subject must be first person. I guess it is a humble form perhaps, and therefore probably used in more formal situations than 거예요. On the other hand 거예요 can be used for second and third person subjects, including non-human subjects like the weather. But each can also be used in other situations too. There's some info here: http://www.koreanwikiproject.com/wiki/%EA%B2%A0%EB%8B%A4

갈거예요 means "somthing/someone will be there (hopefully)" while 가겠어요 implies that the person speaking will be there at his/her own will. examples: 제 동생은 내일이나 모레 집에 갈거예요. My (younger) brother/sister will be going home tomorrow or the day after. 저녁 사 주신다고요? 네, 18시 전후로 가겠습니다. Are you inviting me to a dinner? Yes, I'll be there around 18 o'clock.

갈거에요 is "I will be going", "I am going", etc. 가겠어요 is similar but perhaps less common in casual day-to-day speech and as Jake said, it has the underlying tone of "willingness" that 갈거에요 lacks -- and I would also like to add that it has a "promising" tone that 갈거에요 doesn't necessarily have. *Pronunciation Tip: In everyday speech, Korean phrases containing -요 at the end are often pronounced like [-여].

I think they are totally same.