Solution: Observing the sequence 1, 2, 4, 8, 16, ...,
we notice that: $a_1=2^0$, $a_2=2^1$, $a_3=2^2$, $a_4=2^3$, ...,
Therefore, we can conclude that one general formula is $a_n=2^{n-1}$.
Hence, the correct choice is $\boxed{D}$.
By observing, we can induce its general formula.
This problem provides the first few terms of the sequence, and the key to conjecturing the general formula of the sequence is to explore the pattern of each term and then make a guess.