Pedro Russo said:
One RTS that is quite scalable is Sins of a Solar Empire: Rebellion or Command & Conquer 3 + Kane's Wrath.
I just want to say Sins is a very good game but it is more of a 4x(more so in its pacing and map style) than an RTS so depending on fast paced you(The OP) wants the games I might give Sins a miss. It can be quite slow and I'm not sure I'd call it newb friendly but I wouldn't dismiss it without seeing a Let's Play or something on it to see if you like the style and pace.
Populous: The Beginning is a good but old RTS game that is a bit of a pain to run as you need to close explorer.exe. That said it is quite newb friendly. Dawn of War 1 and 2 along with the Battle for Middle Earth games can be quite newb friendly.
The only thing I would say against them is in DoW 1 playing skirmish you need to get used to teching up(researching upgrades so you can build more buildings and units and upgrade exist units) quite early as the computer gets vehicles relatively early on almost always. It does follow a more Traditional RTS structure. Online is non existent for this game.
DoW 2 does not and is almost exclusively focused on units, territory control and how you use them as opposed to building an economy with a self built base. Also the online versus players is usually quite fast paced.
BFME games are also good but against the comp at higher levels you need to be expecting and early and constant rush of a ridiculous amount of troops.
Edit Also the person below me reminded me of the CoH games and I will also recommend those games as they are quite good and easy to get into. Similar style of play as DoW 1.