1. Color Correct. good old standby. Due to a bug I found in the 2d histo node, I've moved over to using the CC Curves a ton for my clamping and histogrammy activities, and I don't know that I'll go back. For one, you can easily round off your clamps, which is always nice, and two, you can do much saucier things than you can with a histogram. Bonus for the front-back matching and still being a relevant node a decade or so later.
2. Sapphire Warps. Bubble, again, specifically. I bet you could build some reasonably not shitty looking flames by stringing a few of these together. Later today I'm going to take a swing at making steam out of them.
3. Colored Frame. It's not very powerful, but it's so effing useful. Desmond Hume isn't my constant, these guys are.
4. Action. The Paul Newman of flame nodes, which is to say it's had a long and awesome career but it should probably retire and let some new talent shine. Since there is no new talent (fingers crossed for NAB) he's still out there, giving us "Slapshot 3" or wherever that analogy goes.
5. Batch Paint. Really, you should use it. You can even justify doing roto in it (only for very high motion cos it's swiiimy) because it is editable.