-panzer elite is prety cool, ww2 era tank sim(prety realistic but kinda hard at first)
-steel beasts is a lot like panzer elite but deals with more modern equipment which makes it a bit harder than panzer elite because of all the modern equipment / targeting systems
-any game in the combat mission series, they're strategy games that focus on combined arms small unit tactics (platoon level up to about 2-3 battalions in the larger scenarios) there's are demos available at
battlefront.com. barbarossa to berlin deals with the east front , beyond overlord deals with the western front and afrika corps is north africa , crete and italy. i would highly recomend cmbb and cmak these are prety much the only games i have played for longer than a month in many many years. cmbo while good is starting to be a bit dated the graphics are so-so and the other 2 have more options/tweaks that make them more realistic. its hard at first because of the historical accuracy but this is also what makes it so great.