Are there any nice graph classes for which the tree-width $tw(G)$ is upper-bounded by a function of the clique number $\omega(G)$, i.e. $tw(G)\leq f(\omega(G))$?
For example, it is a classic fact that for any chordal graph $G$, we have $tw(G)=\omega(G)-1$. So, classes related to chordal graphs could be good candidates.