C&C Series (Except C&C4), probably the best base building RTS I've every played, especially RA2, RA3 and C&C3
The original Dawn of War was also awesome, especially the Dark Crusade and Soulstorm standalone expansions, even though the game is pretty unbalanced
The Earth Series (2140, 2150 and 2160) are excellent games that not a huge number of people I know have heard of that I would strongly recommend
Age of Mythology is probably my favourite out of the Age of games, but try the others. Star Wars galactic battlegrounds is basically AoE2 in the Star Wars universe so if you like the Age ofs I would recommend it
Rise of nations is also quite good, although it gets a little dull and repetitive after a while
Universe at War : Earth Assault is also good
Personally I found that Sins of a Solar Empire, Supreme Commander (1&2) and Starcraft (1&2) got very boring VERY quickly (especially sins, which was fun for less than a day)
Hope this helps
