Age of Empires 2 (do NOT play 3, the 10 year old AoE2 is much much better)
Rise of Nations
Europa Universalis 3
Sins of a Solar Empire
Total War games are good but they're not RTS
Even though AoE3 is cool, I'd have to agree, something about 2 is just...amazing. But, I bought 3 for 10 cents, so it really made no difference to me if it was good or bad.
Money can't buy happiness. Just video games, which make me happy.
As lots of old and new RTS games have already been mentioned (my most favourite will always be Dune II - the game that started it all), my own recommendation is not a classic RTS franchise, but an economic/city-building sim franchise with real time strategy elements, which I find more intriguing these days than mere RTS, as I love the building/economic aspect of these "real time" games:
Anno 1701 (which is called A.D. 1701 in NA and still looks good even 5 years after release)
or its successor Anno 1404 (aka Dawn of Discovery in NA)
Ever since The Settlers franchise started its slow decline, the Anno series became the more successful (and the imo better) one of the two German big economic sim franchises, which are both owned by Ubisoft now.
Still, The Settlers II from 1996 is my most favourite game from this specific genre (economic sim with RTS elements). As the game was enormously successful in the German speaking area and by far the most popular among the fans of the series, a very good Settlers II 10th Anniversary Edition remake was released a few years ago:
If you're strictly interested in classic RTS gameplay though - i.e. focus on combat - my vote goes also to Ensemble Studio's brilliant Age of Empires II and Warcraft III (Warcraft is my most favourite Blizzard series). Easily two of the best RTS games ever made. Don't listen to the people though, there's nothing wrong with playing Age of Empires III, it's a good game, but like others in this thread I'd recommend to at least give Age of Empires II a try despite its, well, age.
In my opinion, Company of Heroes is probably the most in depth and detailed RTS I've played.
But my favorite RTS is Age of Empires III: The Asian Dynasties. One, because its got a lot of unique ideas for the genre as a kind of mix of Age of Empires II and Age of Mythology with a 'deck' system added. Two, Because it seemed to fix every problem from Age of Empires II (refreshing farms, unit AI, more unique ships, hero units for exploration, etc). And three, because I'm actually good at the game.
I feel its really sad that AOEIII never took off. And I attribute that mostly to the 'sequel effect' and people not wanting to get off AOEII. Same thing as Smash Bros Brawl, FFVIII, Chrono Cross, etc. However, having said that, I know there are other reasons the game didn't take off. ES Online is REALLY laggy and MS put some rediculous piracy protection on the game so even two people with the same build of the game fresh after install will get a 'RCR Mismatch' error and can't play the game, on LAN of all things. Also, the game was released in parts and didn't become the awesome game it is now until the Asian Dynasties expansion.
Anno series is awesome if you prefer a more complex resource management. I recommend this because you're saying you played Stronghold a lot. IMHO, Anno series is much better than Stronghold.
