The ones from Fireboard are well thought out. Each one will hold two probes and ensure your probes don't get tangled. Of course, you could just coil your probes and put each in its own plastic bag, but the FireBoard holders look cooler.
Join the fireboard group and search for the guy 3d printing them. He does custom design and they appear to be much more practical than the ones Fireboard sells. I have the standard Fireboard ones and am not a huge fan of them and the two probes per holder, others love them. The 3D printed ones are a good value and he does them custom to sports teams, schools, names etc.