Consider donating to Coalition for the Homeless of Houston, which is doing tremendous work to help those displaced by the storm.
While there are plenty of national organizations helping with the relief effort, groups with strong ties to the local community are most effective at the ground level. Coalition for the Homeless of Houston has a 4/4 rating on Charity Navigator. https://www.homelesshouston.org/take-action/donate/
Explore other options at Vox: Hurricane Harvey: where you can donate to help with disaster relief and recovery