If you can find it anywhere, I used to use a product called Paul Brown Hawaii Stay Straight. It was great for use with a blow dryer, and even better to use if just air drying (or using diffuser), because it was all botanical and would just bind the curls together nicely. I stopped trying to source it because it got too hard to find.
I have since found, and stuck to, a product called Moisture Mud, made by a local hairdressing salon called Istashi, in Belgrave South. They can post to anywhere in Australia. 500ml costs me $19 and it lasts me for at least 3 months. You can use it instead of conditioner, or just after washing. I take it to the beach and pool. Same effect as the Stay Straight, just not as botanical...or expensive!
I have extremely thick, curly hair that tends not to bind into defined curls, so I need something like Moisture Mud to help me out there.
Since having Oscar, though, I found that as my hair grew back after the 'falling out' period, it is growing back in a tight curl like never before...it's like a ringlet, which I am quite excited about - at last, some discernible shape! I don't know how long that will last, as my hairdresser says that my normal hair will grown soon. Geez, I hope not...
Also, my hairdresser (different from where I get my MM), has a great technique that he is renowned for locally. Instead of cutting and shaping with scissors, he uses clippers that he designed. On all hair lengths. Particularly effective on my hair because it thins out the bulk of my hair, without leaving short wispy bits underneath, the way that traditional thinning does. This helps with styling my difficult hair like I never thought a haircut could.
I also second Nixonsmama's suggestion of rinsing in cold water, especially in humid conditions!