crepe myrtle trees and hydrangia bushes
Crape myrtles can be pruned now until new growth begins in the spring. Depending on the variety of crape myrtle you have will depend on the amount of pruning it will need. Most crape myrtles do not need near as much pruning as people give them. The tree varieties (15+ feet tall) don't usually need pruning. The rule of thumb for any variety of crape myrtle is to prune branches back to where the diameter is no larger than a pencil. Below is a publication with additional details and I have included a picture demonstrating proper pruning on a tree form crape myrtle.
As for hydrangeas, it also depends on the hydrangea species you have. If it is a bigleaf hydrangea (also called mophead or lacecap) or an oakleaf hydrangea, you would not prune until after the plant has bloomed (typically in May/June). You can go in and remove any old branches that are dead to open up the canopy - see before and after photos of bigleaf hydrangea thinned. If it is a smooth hydrangea or peegee hydrangea (both of which bloom in the summer) you can prune those back now.
For more information, see article below.