Quantum query complexity and certificate complexity
In the paper Negative weights make adversaries stronger, Lee, Spalek, and Hoyer give a function for which $ADV^{&#177;}(f)= \Omega( ({C_0(f)C_1(f)})^{0.549})$, where $ADV^&#177;$ denotes the general adversary lower bound. This lower bound has since been proved to characterize quantum query complexity. 

This function is obtained by composing a function on a few bits bits with itself $d$ times. You get in the end $C_0(f)=C_1(f)=3^d$ and thus $C(f) \in o(Q_2(f))$.