Unfortunately, RTS'es had their best time in the early 2000's. Starcraft 2 is the easy king of the hill because there's not much competition. But there are some games. Let's see...
* grey goo. From former westwood employees. I honestly couldn't get into it
* rise of nations: this is an old one (2003), but to me it's better than age of empires. It's probably best to consider this a mix of AoE with civilization. It has real time strategy, but in the earlier ages you can't effectively attack your enemy because you'll lose health when going outside your territory. Meaning: you've got to research and harvest a lot. One of the things I like most is that if you advance ages faster than your enemies, you can get into hilarious situations where you have tanks while their "army" consists of horses and spear guys.
It has a "world conquering" campaign, but IIRC it's more a series of skirmishes than the classic "here's one or two extra toys to play with and an interesting mission" structure.
* ashes of the singularity: escalation. The scale on this is pretty large, but I rather enjoyed this one. Haven't played through the entire campaign, though.
* supreme commander. I started off on the wrong foot on this one (long story). I can see why it's good, but nonetheless, I couldn't get into it enough.
* planetary annihilation: titans. This reminded me a lot of ashes in the large scale of things (but on entire planets, this time). Pretty fun, but the campaign bored me after a while
...and one a bit "off category":
* offworld trading company: this is a weird one in that it doesn't have weapons. And yet I have to agree with reviewers. On the surface, it might SEEM like this is a bit of city building and/or civilization (ooooh...exploring mars!) the game is extremely cut throat (but in an economic sense). As a result, it feels more like an RTS than quite some other games. It's not exactly taxing on any modern PC, though.