Looking for help with a Esterification Lab - Chemistry?

The esterification process using a carboxylic acid is a reversible reaction, and often reaches equilibrium with large amounts of starting material still present. What are two classes of reagents other than carboxylic acids that might be used to make this an irreversible reaction and drive the reaction forward, towards completion?   

I am having a little bit or trouble trying to identify irreversible reagents. Appreciate any help !