So you've decided to start the rewarding hobby of miniatures wargames. Now that you have the figures, the natural question is what do I do with them? Obviously the intent is to game battles, but what rules should one use?
Depending on the period you focus on, there are a plethora of rules available currently. In many ways wargaming is in the "Silver Age" (to borrow a comics reference), with a resurgence in rulesets, quality figures and interest (as opposed to the "Golden Age" of the '60s to the '80s, when the industry was dominated by rules from Featherstone and Bath, with figures from Minifigs, Scruby and others).
I use a variety of rulesets, depending on the era I wish to play:
For Ancients (and here we'll use the "wargamer" definition and limit Ancients to the periods between 3000bc to 1500ad), I am currently enamored with (in 15mm) Might of Arms and Fields of Glory. Both use "element" basing (that is, multipe figures on a single base or element), and try not to simulate combat from a loss basis but from an effects basis (it is top-down rather than bottom-up). While I vastly prefer MoA for its "psychological" approach to armies, FoG is currently very well supported, with its own line of army books and a very slick website. Other rules that exist include De Bellis Magister Militum, De Bellis Multitudinous, De Bellis Antiqitas, and others.
For 25mm Ancients I vastly prefer Warhammer Ancient Battles. The advantages of this ruleset is that the Warhammer rules are well known outside the historicals arena (making recruitment a bit easier), the rulebooks are very well published with lots of good photos of minis, and the army books tend to be very informative besides being a simple list. In this way, the game very much is inspired by its fantasy counterpart. For someone that does not know anything about the history involved, the books can be a very good introduction to the period.
On the downside, Games Workshop recently dropped the Warhammer Historicals imprint and will be devolving game support to Forgeworld. How this will pan out no one really knows. The hope that with the new edition of the game, it will continue. However, if the game collapses due to Forgeworld's mismanagement, the game that almost single-handedly created the 25mm figure rennaisance in historicals will be a sad loss...
Finally, in the historicals arena, I tolerate Flames of War. Again, basing itself on the commercial model of the Warhammer game, Flames of War tends to be very pretty, and the rules easy to pick up. The downsides are that the game sometimes plays a-historically, and of course there is always the occasional German player with maxed out King Tigers.
On the Fantasy/SF front, I also enjoy the well known games Warhammer Fantasy Battle as well as Warhammer 40,000.
Finally, no blog of mine is complete without a plug for Battletech. A game that has been going for 25 years, and has arisen from its supposed death more popular than before, Battletech is a game that has stood the test of time. While not strictly a miniatures game, it is very well supported with a minis line, and so I include it here for that reason.