I will tell you this --- Without these tools, I would not be knitting lace. It would be too frustrating and annoying. Seriously.
The first indispensable tool is a row counter. I have 4 of these red ones and one of the little green ones. If you care which row you're on, you need one of these.
The second indispensable tool would have to be stitch markers. I wouldn't even try to knit lace without these. Place them between each repeat, and you just have to worry about that repeat. You also become aware of problems more quickly. Don't make lace knitting harder than it has to be.
The third indispensable tool is my Chart Keeper. I swear I would lose my mind without this, and would definitely lose my place.
I found this one at Michaels. It was marketed towards cross stitchers and crocheters. For such a useful tool it was relatively cheap too. I got this one for $9.99.
Here it is in use---
You place the magnets so you can keep track of where you are in the chart. I put the two smaller magnets on each side of the repeat that is knit several times within one row.
Speaking of lace knitting, it's time for a Hanami Stole update ---
I have now finished Chart B. It's coming along nicely, and will be very luxurious to wear. I can tell already.