Not necessarily how it should be, but my button opening range is:
{22+, Ax+, Axs+, Kxs+, 54s+, 64s+, 74s+, 87o+, Any two broadway cards}
Of course that'll get modified based on blind tendencies. From the small blind you need to be tighter, because you're playing the whole hand out of position. You need to rely on strong intrinsic value of the cards to help you overcome your positional disadvantage.
My goal is to play a similar range to my UTG or MP range, however in my opinion I tend to be too loose from the SB.