When you get right down to it, white must move the d pawn sooner or later. It can either go to d4 (characteristic of the Open Sicilian) or it can go to d3 (characteristic of the Closed Sicilian).
With that said, on d3, the pawn blocks white's light squared bishop so white must make other arrangements in order to castle kingside. There are two main ways that this can be done - either white can move the bishop to c4 or b5 before moving the d pawn, or white can fianchetto the bishop.
So to bring this answer back to the specific question, white has a few concrete options that avoid d4:
- Rossolimo/Moscow (
3. Bb5 vs
2... Nc6 /
2... d6 respectively)
- Grand Prix Attack (
1. e4 c5 2. Nc3 Nc6 3. f4 g6 4. Nf3 Bg7 and either
5. Bc4 or
- Closed Sicilian (
1. e4 c5 2. Nc3 Nc6 3. g3 g6 4. Bg2 Bg7 5. d3 d6)
Surprisingly, almost every other Sicilian variation for white either involves white playing an early d4, or is very similar to one of the above. For example, the King's Indian Attack is really a variation of the Closed Sicilian (alternatively, the Closed Sicilian can be considered a variation of the KIA...).
Finally, the Wing Gambit merely defers d4, as does the Alapin. While white can always choose to omit d4 (
2. Qh5?! would be an extreme example), these are generally considered dubious sidelines played at white's own peril.