Besides determining what type of player they are (LAG, Calling Station, Rock) by how many pots they see and how much they bet, I think betting patterns can tell you a lot.

I think the combined experience of the people on this site could put together a good list of typical betting patterns and what they mean. I will try and put together a list of some betting patterns I have noticed (at low buy-in levels). This is simply my opinion, interested to hear any disagreements or additions. Besides simply the pattern and what it says, I will give it my best guess at a reliability rating.

Action: Preflop there is a third raise. Means: AA (or at worst KK). Reliability: 100%.

Action: UTG with relatively short stack (less than 8x BB) bets 2x BB. Means: He has a monster (AA,KK, AK). Reliability: 99%.

Action: Scary flop, you bet out and called. Villan calls until river when he raises you significantly. Means: He was slowplaying you. Reliability: 80%.

Action: The flop pairs (QQ8). Someone bets a reasonable amount. Means: They do not have a Q. It seems almost everybody slowplays trips. Likely have an 8 or high cards (especially if bet is from late position) Reliability: 66%.

Action: Flop paired (JJ8). You bet, he raises 2x your bet. Means: He is likley determining whether his pair of 8's is any good. If he has set, he likely would just call. Reliability: 70%.

Action: Two to flush on flop. You bet, small to medium stack goes all-in. Means: Flush draw. Reliability: 66% (Although I have made a lot of money by playing my two pair or better by check-raising all-in in the same manner in order to get weak TP or middle pairs to call believing I am on a flush draw. I think this variation is becoming more common.)

Action: You bet 1/2 pot or better on flop with TP and they immediately double your bet. Means: They can beat top pair and are looking for you to call. Reliability: 80%.

I am sure there are many more which I would be interested to hear but that is what I can come up with initially. If someone disagrees with what the bets mean or the reliability I would be very interested to hear it since sometimes I think I play too weak-tight.