All-in in No-limit Holdem Cash Games

All in: It's the most exciting phrase in poker, and one particularly suited for Texas No-Limit Holdem, where you can put all those chips in any time you want. When should you go all in during a Texas holdem cash game?
Unlike in Texas Holdem tournaments, where an all in can potentially end an opponent's life in the game (or your own, for that matter), moving all-in in a cash game can only put what a player has on the table at risk (or as much as you have on the table, if he has more chips than you). This means you should really think of an all in as simply the largest bet you can legally make.
You will notice that in Texas Holdem freerolls, players often move all in regularly, In an attempt to either amass a lot of chips, or spare their time.
During a no-Limit Texas Holdem cash game, there are a number of reasons you may decide to move all in. Below are a few things to consider.

You Don't Want to Make any More Decisions

Once all your chips are in, no one can bluff you. Either they call and make the best hand and win, they don't and you win or they fold. In this position, no one can outplay you. If you aren't sure how you will proceed on the turn, but know you want to play the hand, you may choose to move all-in.
For example, in a $3/$6 blind game where you have a stack of $175, an early position player raises to $18, a middle position player calls and you call on the button with Kc 9c. The flop comes Ks 8s 3h. The big blind throws $20 into the pot of about $60, and the middle position player raises to $60. Now you have a decision. You can certainly fold.
However, you may feel that the early position player is making a continuation bet and the middle position player is on a flush draw. If you flat call, it will be very difficult to know what to do on the turn. If a spade comes, you will probably have to abandon the hand, and even if one doesn't come and someone bets again, you won't know if they have a King. If you make a minimum raise here and someone calls you, you will have very few chips left to work with anyway.
Here you may want to move all-in. Ideally, the early player may fold a KT or better fearing the raise and re-raise, and the middle player will call with bad odds to try to hit a flush.

You Have a Hand that is Strong, but Vulnerable

A hand like AA is great in Texas Holdem, but it has little chance to improve and when it does, it often kills the action. A popular strategy with AA is to make a modest raise before the flop to build a decent pot, and then move in on the flop if nothing too scary comes. Every card that you allow opponents to see puts your hand in jeopardy, so an all in to end the hand right away can be preferable.
Similarly, if you have 8 7 and the flop comes K 8 7, an all-in check raise is a popular move, since you are probably best, but vulnerable to a lot of hands. Here you are hoping to get called by a hand like AK, and get hands like flush draws and straight draws to go away.

You're Bluffing

You hold T9 and the flop comes T J 8. A pre-flop raiser bets out and you call. The turn is an A. He makes a pot sized bet and you call. The river is a K. He checks. This is a tempting situation to move all-in. Even if your opponent has a set, he has to worry that you might hold a Q, or even have been trapping with KQ. He may be confident you are bluffing, but you have to be made of strong stuff to call off all your chips on a hunch.
Of course, if your opponent has the Q you are sunk, but you will have to rely on your read to determine whether that is likely. This can be quite tricky when you play Texas Hold'em online, but there's always that old intuition to work with.