Glest is a freeware RTS game, and it has fairly good graphics for being a free game!
http://www.glest.org/en/downloads.html

Castle Defender another good freeware game, it's not that hard, but it gets tougher near the end.
http://darkcoder.co.uk/Castle%20Defender.rar

WarCraft III I'm sure you've heard of it, if not, then download this to get a taste of RTS!
http://ftp.blizzard.com/pub/war3/demos/W...taller.bin

StarCraft, made by the same company that made WarCraft (Blizzard duh!) It's like the futuristic version of WarCraft, except the graphics aren't as good, but the gameplay is still there. Another RTS to definitely check out. It might even work on your old PC.
http://ftp.blizzard.com/pub/starcraft/demos/SCDemo.exe

Army Men RTS, kind of like WarCraft but with green army men, and guns.
http://www.download.com/Army-Men-RTS/300...56819.html

War Hammer 40,000 Dawn of War an intense RTS.
http://gamefiles.blueyonder.co.uk/blueyo...a_demo.exe

LOTR - War Of The Ring, similar to WarCraft but with LOTR, it's a pretty good game, and a lot of heroes to train.
ftp://ftp.farlep.net/pub/clubix/demo3/wa...g_demo.exe

*More games when will be added when I have the time. If the links don't work reply, and I will try to find working ones. Also if you know any other good RTS games that are freeware or have a demo out, reply and I'll edit it into the first post.

Last updated on 5/13/2007 if you liked the post, feel free to Digg It!

Enjoy ;)

Add World In Conflict;

http://demo.worldinconflict.com/us/

CoH - Company of Heros

This is a great RTS. I love the fully destructable buildings to go along with the great game play. Like other RTS games you start off with the more basic units and build your way up.

http://www.fileplanet.com/167354/160000/...eroes-Demo

I second Company of Heroes. It helps that I've found the CoH community over at gamereplays.org to be fantastic, mature, and friendly.

im wondering if red alret 3 has a demo out atm. thats a really good rts. although im not the best rts player, i had to go out and buy it the day it came out.