The Way of the World is filled with characters that are driven by cynical self interest. Which characters contradict this attitude and perform generous acts?
This is a brilliant question to consider, as actually so many of the central characters are shown to be incredibly selfish and acting for their own interests, and even characters that we like and are presented in "good" ways show that their governing trait is their own selfish desires and wants and their willingness to do anything to achieve their ambitions. This is why characters such as Mirabell, in spite of his attractive nature, does not fit your criteria as she shows himself willing to do anything to gain what he wants.
Perhaps one character we could look to therefore is a minor character, who nonetheless plays an important role in the plot of the play. Foible, the waiting woman to Lady Wishfort, helps Mirabell in one of his schemes to trick her Lady. However, she is one of the few characters in the play who act out of something more than self-interest. She gains nothing by tricking Lady Wishfort, and she does it in the name of love. Nobody is injured or hurt because of her tricking, and thus she is pardoned at the play's close.
In addition, let us remember that it is thanks to Foible that the schemes and stratagems of Fainall and Marwood are exposed and Lady Wishfort is protected from having her wealth stolen. Although Foible is not above acting for her own advantage, as she gains herself a husband through supposedly looking for a husband for Lady Wishfort, at the same time these two examples show excellent ways in which she acts generously for the benefit of others in the play.