The Atari Axis and Allies is entertaining for a bit, but then you see how unoriginal and uncreative it is.
For WW2 RTS, I like:
Sudden Strike - pretty fun, no base building, just attack and destroy with a variety of units. You can probably find this in a bargain bin or budget software rack for $10 or less.
Company of Heroes - This is probably one of the best RTS and best WW2 RTS I’ve ever played, but it will take a decent system to run. It’s very fun, well done, and they just released another scenario that is stand alone or a continuation of the original.
Commandos - This is probably best described as an RTS, but you only control a handful of guys that are specialists in certain things. I played the first and it was quite polished and fun.
Close Combat - A series I hold dear to my heart and has never really let me down. Probably the best one is A Bridge Too Far, but the russian front one is good as well, and D-Day is decent.
For all RTS:
Age of Empires - The second one is great, especially with the add ons. I loved playing multiplayer and the campaign. One of my favorite things to do was play 2 vs. 2 (with three friends) but have only 1 civilization for each side, so you and your partner control all the same things. I played the third as well, but for some reason it feels pretty different.
Age of Mythology - More recent than Empires, it includes a fantasy angle like monsters, heroes, and gods/titans. Pretty fun with a little spice.
Command & Conquer - Can’t really go wrong with this series.
Starcraft - Pretty good, but very generic. I honestly don’t see why it is so popular, except that it appeals to the lowest common denominator.
Majesty - An interesting take on RTS, where don’t directly control your heroes. You’d have to play it to understand.
MechCommander - Older, but was fun. Kinda hard too.
Myth/Myth2 - Well done, and a blast. Avoid the third though.
Rise of Nations - Pretty standard, but good.
Total War - This series is very good, and gets better and better. Shogun is the one I have, and it’s loosely based on the board game (now called Samurai Swords). It’s got a balance of RTS battles and empire upkeep.
That’s about all I can think of right now.