Plenty of others have commented on speakers that work and what to look out for, but you may also want to look into creating your own mounting bracket to allow you to fit basically any reasonably 6 3/4" speaker. For my initial speaker install I just bought a pair of 3/4" MDF rings and mounted them to pieces of sheet metal, then screwed that into the mounting holes in the door for the stock bracket. Allowed me to mount pretty deep front speakers in the door without issues. I later had a shop create a much nicer bracket for the speakers. They also put a material called Frogzskin around the basket of the speaker to keep water out.
New (shop created) mount: