Hmmm, some interesting stuff their to seek out.
I did a bit of surfing on the Mile High site and discovered some interesting things.

Time Warp look like a must have with its Mike Kaluta covers and interiors by Don Newton, Howard Chaykin and Steve Ditko.

All-Out War looks cool too with the great George Evans doing pencils on Viking Commando of all things.
What else did Evans do at DC? I know he did some war stuff too.

I never realized that in the 70s and early 80s, DC had much more diversity than Marvel in terms of different genres. They had mysteries, war, westerns, science-fiction, whereas at the time Marvel just had a steady diet of superheroes.

How many mystery anthologies did DC actually have throughout the years?
These are ones I know of:

House of Mystery
House of Secrets
The Witching Hour
Unexpected
Tales of Haunted House (sic?)

How much of that stuff has been reprinted in Showcases?