僕 が 神 だ — Tae Kim's Japanese Grammar flashcard

It's ME who's the god (and not someone else). The emphasis of "boku" also becomes clear from the intonation of this sentence (press "r" to play the audio again), but that's not always the case.

kami: god

Note that the emphasis "ga" puts on the previous word may not always be as strong as in these examples. For example, "ga" is often used to introduce a new topic that hasn't been mentioned before. Therefore, Tae Kim also calls it the "identifier particle".