Right Triangle Congruence
HL, HA, LL, LA Theorems
With the exception of H-L, most of these aren't covered by most teachers because they're not really necessary. If your class does use them, though, this video will explain what they are and how they're derived from SAS, ASA, and AAS.
HL, HA, LL, LA Proof Examples
Full proofs using these most special of right-angle theorems. Don't watch these if your class doesn't cover them, though, because you won't be allowed to use them on tests.