I'm inclined to consider SRPGs/TBTs kind of their own thing that isn't quite what is usually meant by "Strategy" as a genre, but if we are including it then there are some definite all-time classics there;

X-Com: UFO Defense
XCOM: Enemy Unknown/Enemy Within
Xenonauts
Vandal Hearts 1 & 2
Front Mission 3 (It's sooo good Del you're in for a treat it only gets better)
Basically all Nippon Ichi games

Huh I guess I already said Jagged Alliance 2 and SS2. Welp, guess my considerations aren't all that rigorous anyway