For PDF copies of Migne’s PG, I’ve been using Documenta Catholica Omnia, which has image scans of the actual pages.

The Patrologia Kleida site seems to have been down for a while, but a renewed version of its texts have been put on another site:

Listed by Volumes:
Listed by Author:

The texts here only have the Greek, but it is searchable.  Some have noted bits that are missing but another great online resource if you just want to check something quickly.

HT: Roger Pearse