I've ignored most turn-based strategy games, as I don't really want to play the exact same game as a normal boardgame, and I've tended towards more accessible titles - ones you might be able to con your kids/spouse into playing with you. I've also excluded shooters (that may require good - aka young - reflexes) as well as overt RPGs as they don't really fit the wargame-esque genre I'm trying to focus upon.
The Total War series are not only good strategy games, but some of the best PC games ever made.
The Total War Series ($20ea)
These amazing games have two levels - a strategic turn-based level where you can build castles, raise units and travel to foreign locals (and then kill them). Then you fight battles in real-time. Your commanders have a RPG aspect to them, as they gain skills and attributes (sometimes randomly, sometimes as a result of their actions in battle). There are 3 noteworthy games:
Medieval 2 - awesome medieval warfare from 1100-1400. My favourite, but solo only.
Napoleon/Empire Total War - muskets and all that from ~1800. Empire is worldwide (i.e. Indian Wars etc) while Napoleon is focussed on Europe and allows you to fight with/against friends. Also allows you to fight age of sail naval battles.
Shogun 2 - Unsurprisingly, this is about becoming Shogun of Japan. Also allows you to play with/against friends.
These games have lots of "mods" - game files you can copy & paste in order to transform the game - i.e. Medieval 2 can be modded so you can wage war Middle Earth.
World of Tanks (free)
The ultimate "Dad game"- you only need to learn a few buttons to play. It's a simple concept - a 12v12 deathmatch with WW2 tanks from all nations mixed up. It's simplicity is chess-like - experienced players who can angle their tanks armour, hull down and ambush effectively can swing a game. Although the game is free you may have to play 100s of hours to get a specific tank depednign on their power (i.e. a Tiger might take 100s of hours and a Pz. 38 only an hour to "unlock.")
IL2: 1946 ($10 + $30 joystick)
I haven't really found any "good" aerial wargames. Luckily I have Il2:1946. 400+ planes with historically accurate performance and detail. You can make your own missions. Even better, you can change the difficulty from super easy to full simulation. Note: a cheap twist-stick joystick is necessary.
Rise of Flight (free, + joystick)
The WW1 aerial game. You get a few planes free, but need to pony up ~$10 per plane if you want more variety. It's simple to fly (WW1 planes weren't known for their complexity.)
Wargame: AirLand Battle ($20)
A brilliant modern game based in 1985. Recon is very important as is air defence and protecting your supply trucks and command vehicles. Red Dragon is a newer version of the game with warships added, but is not quite as well balanced.
Mechwarrior Online (free)
3 lances (12 mechs) per side face off, to capture areas or destroy enemy mechs. Only your first mech is free - the rest cost ~$10 each or many hours of gameplay to "earn" them. If you love Battletech and customizing mechs but don't enjoy the record keeping, this is the game for you. You control a single mech, in a game that is more a sim/slow paced shooter than a tactical game. Teaming up with friends isn't recommended as you will be put into the "competitive" league.
Warhammer 40,000 Dawn of War ($20+)
This allows you to play 40K in real-time. A surprisingly good game - but expect to pay $15 for "expansions" as the original game doesn't have all the factions. Games Workshop - oh how we love you. Can play multiplayer games as well as single-player campaigns.
Company of Heroes ($10)
Pretty much Bolt Action on a PC. Also uses the same engine as Dawn of War. It''s a better game than its sci fi counterpart. Also needs an expansion ($10) if you want to use British troops.
Men at War: Assault Squad ($20)
The hardcore WW2 platoon game with more realism than CoH. There is a Vietnam spin-off, and a WW1 version is being worked on.
Sins of a Solar Empire ($20)
A space strategy game. It can get a bit "blobby" when fleets get big - kinda "throw everyone in to the fight" but AI allies actually help you which can make for some cool 3-way fights. Multiplayer as well.
Silent Hunter III ($10)
Amazing sub-sim - roam the entire Atlantic looking for convoys. Difficulty can be changed, and there are some impressive updates available online such as Grey Wolves which significantly update the graphics and gameplay.
X-COM: Enemy Unknown ($20)
I promised no turn-based games, but X-COM is very accessible, and allows Mordhiem-style progression as you upgrade your squad which is tasked with rooting out alien incursions.
Running with Rifles ($10 on Steam)
Cos running with scissors is for sissies. Remember those plastic green, brown and grey army men you had as a kid? This game makes you one of these army men. You control a single guy and a squad of friendlies, as you try to influence one of the many battles that rage over capture points. You aren't "special"or "the Chosen One" and your abilities are the same as the other 300 guys- you're just a little guy in a big war. Unexpectedly deep game. You will be overconfident, and you will die. Repeatedly. Cartoonish graphics, amusing speech bubbles - great fun, especially with friends.
ADDED: Homeworld ($10)
An awesome RTS in space with real 3D warfare. A bit long in the tooth now, but vertical battles , protecting your mothership and mining ships whilst scouting and raiding your opponents = awesome fun. Wings of fighters zipping around, an interesting mix of spaceship classes - I don't think it's strategic spacefleet combat has ever been beaten.
As I glanced down at the prices I realised how much we play wargames for the hobby/tactile aspect of it - it certainly does not make sense financially! Imagine being able to buy every Warhammer army for a total of $40 - or even 400+ 1:300 aircraft for $10.... and being able to change paint schemes at the click of a button.... It's even easier to "meet up"with friends and game online from home. (Which is why I don't understand people who field unpainted minis - if they don't care about that aspect of the hobby,why are they even playing a miniatures game?)
Anyway, the purpose of this article was a "tester"to see if there is interest (either in comments, or by number of hits) in doing a few PC game reviews - or even simple "at a glance" two paragraph summaries of how gameplay works.
ADDED: Feel free to "friend" me on Steam - evilleMonkeigh
Steam is the #1 online service that allows you to buy games digitally, and also network with other players. It's very polished, popular and professional, and they often have sales with 50-75% off as well as many excellent free games. I highly recommend downloading Steam (it's free) if you do any PC gaming at all.