If the copy of Minesweeper that comes with Windows isn't enough for you, you might want to check out Ruckus Buck's Dangerous Mines. This game is Minesweeper with a few more options. The main point of the game is still to sweep through a series of tiles and logically deduce which tiles are free and clear, and which ones contain bombs. You'll use the right mouse button to flag the tiles with bombs.
In addition to the game's basic mode, there is also a timed mode and a "free edge" mode, which gives you bomb-free outer rows and columns. If you like, you can connect to an online server, but all this really does is let you see a chat room while you play. There are usually only a couple of people doing this, and they all seem to be the quiet types.
For most, the stock Windows copy of Minesweeper will be more than enough. But if you're a minesweeping fiend, Dangerous Mines' additional modes might be enough to keep you entertained.
