Homeworld 2, but it does not have land battles, but fleet battles are pimp.

Also there is that new starwars RTS.

 

Best game ever . No, there aren't any which are exactly like it unfortunatley and it looks like IG III has turned into vaperware.

 

there was a small attempt on Empire at War that just came out, but theres no base building, only land battles. and the universe map is crap.

 

IG III was renamed to "Nexus: The Jupiter Incident" IIRC

Iv played it a few times, i thought it was prity good.

 

i think your best bet would be SW: Empires At War.

It's not as good, but it is similar in a few things and it has added Star wars which is always a plus.

 

Nexus: The Jupiter Incident had a great engine. Lots of flashy fx like camera shake and things. I just found it a bit hard to play so I gave up.

 

I think the best game in that genre myself is Space Empires IV I've played them right through SEII, SEIII and now SEIV

Such an in depth game and take ages you research, put together your own ships, they need refuelling, resupplying, repairing, then you have to decide what needs mothballing, what needs retrofitting, what needs upgrading you have fighters, mines, starbases, construction yards, scouts, cloaks, you can dstroy planets, stars, nebula, you can create new warp gate, destroy them the list goes on

always fun when yoiu're about to be overrun and you simply destroy the warp gate leading to your system leaving you isolated

It is available over Steam as a paid downlaod as well

 

Galactic Civilisations sounds like what you're looking for too. Haven't played it myself, but it got very good reviews.

 

Great game with a good scaleable engine, had tons of fun playing that multiplayer.

 

Woah! Its been years since i played that game! Thanks for reminding me of it :O

*Has a look around at reviews for the games that have been suggested*