This is just an extension of the "POKER DRIVEL: Feeler Bets" post, but it does present another example of how to use small(ish) bets that I think can benefit many beginning and midrange players.
Another use of the half-pot bet post-flop is to take and keep control of the hand, especially when you're on a solid draw you would really like to see through to the end. Say you flop four to a strong flush or an open ended straight draw. If you're out of position, a half-pot bet serves three purposes:
1) It puts the screws to the people acting after you, forcing them to put up or shut up. It's entirely possible they didn't hit anything and will fold to this bet without a fight.
2) It discourages a raise unless they've hit something remarkable.
3) It builds the pot a little bit in case you do hit a big hand.
(BEWARE) A good player can turn this tactic around on you and let you bet into them when they've hit something big. Watch out when doing this against solid aggressive players.
The end result? They're likely to lay it down if they haven't hit anything - or simply call rather than raise - whereas, if you'd checked, they were VERY likely to bet and force you to lay down your draw.
Watch carefully how they respond to your post-flop bet. I find this moment to be telling against many players. I can usually tell whether they were calling reluctantly, hoping their hand is good enough, or drawing me in. Even if you don't hit your hand on the turn, this might be a good time to fire a larger bet if they look like they're also on a draw or don't have a lot of confidence in their hand.
Using this tactic successfully requires some practice and no small amount of caution... If you do it wrong, or against the wrong players, you might find you're outplaying yourself in the end. If you're consistently being reraised, stop using this tactic - then use the same betting pattern when you've flopped a made hand.
Try it out and see if you can make it work for you.