I also love Tenebrae. It took a few viewings for me to have much appreciation for Deep Red. Always enjoyed the violence and music, but it's a little slow at times.

Without knowing what other gialli you've seen, I rec Argento's Phenomena and Opera. I've always ranked them among my favorites of the genre. If it counts as a giallo, there's StageFright (1987).

I find it hard to rec many, especially since you're looking for "the best of the best." I've seen a lot of gialli and while they're not all bad, most of them are far from what I'd consider the best of anything.

You've possibly seen them as well, but there's Argento's early 70s "Animal Trilogy": The Bird with the Crystal Plumage, The Cat o' Nine Tails, and Four Flies on Grey Velvet. While I've always liked Bird the most, the other two are decent.

For some non-Argento:

The Fifth Cord (1971)
A Bay of Blood (1971)
Short Night of Glass Dolls (1971)
What Have You Done to Solange? (1972)
Don't Torture a Duckling (1972)

Admittedly, I might be biased when it comes to The Fifth Cord since it stars Franco Nero. A lot of gialli I've seen I don't remember much about, even some I own and have watched at least a couple times.

One I haven't seen, but I'd really like to and you might consider it as well is Fulci's A Lizard in a Woman's Skin. I often see praise for it.

I hope you'll get some sort of enjoyment out of them.

I don't think of A Bay of Blood as a giallo either, but both IMDb and Wiki list it as one. I'm certainly no expert on what a movie needs to be to count as a giallo, besides Italian.