Just in case these prog metal ones haven't been pointed out around here (they likely have I'm sure): Spock's Beard - "V" and Symphony X's "V: The New Mythology Suite" (bonus for same title and very similar covers!) Dream Theater's "A Dramatic Turn of Events" and Circus Maximus's "The First Chapter"
I sort of hate doing this because copy-catting is so rampant and is as about as common in rock and roll as guitars and drums... but...
The covers are not at all alike, but I noticed they used variations of the same unique font (only the letter "C" is different):
I really do love this thread and there are some truly amazing examples but there are the obvious homage covers and there are others that I simply look at them and think huh?
Well, I was going to say the first Doors album and the first Stooges album, but someone beat me to it. Here's my contribution: Van Halen's 'Fair Warning' (1981) Alice Cooper's 'The Last Temptation' (1994)