If you are looking for just some basic memory, the Corsair Vengeance LP fits under most heatsinks.
They come in 8GB(2 sticks) and 16GB(4 sticks) kits.
Please check your motherboard QVL for memory. sometimes you will be unlucky enough to have memory not work because of incompatibility so it is always best to check the list.
Basically anything without large heatsinks should fit.