If you enjoy games about combat, but don't want to spend an entire weekend recreating all the intricacies of a particular battle, these are my recommendations. If you've never played wargames, start here. And if you want to introduce your friends or families to wargames, start here.
Various U.S. Civil War battles can be simulated in Battle Cry by using modular terrain. Fairly simple rules make it a great choice as an introductory wargame, but the strategy is deep enough that you'll definitely be back for more. Memoir '44 streamlines the already wonderful game system and moves the setting to World War II.
An updated version of Risk, it improves the original by shortening the game (five turns), introducing underwater and space territories, and more. Powerful commanders and cards add new strategy. You can still use the original rules if you prefer.
If you figure it out, there's a definite strategy to play for this game -- but getting there is fun nonetheless. (Don't ruin it by searching the Web!) A&A Europe uses the same basic gameplay as the original A&A, as does another sequel, A&A Pacific.
The art of negotiation is everything in this classic. Set aside an entire afternoon to play, and get ready for some serious intrigue. Who can you trust? Who should you turn on? And when? Moving armies and fleets has never been so tense.
It takes about four hours to play HotW, but the time will fly. Probably best with 5 or 6 players, this game follows the rise and fall of empires through 7 epochs. Players control separate empires in each epoch, vying to end the game on top.