Like the title says. I'm wondering how to make use of filled soul gems. Can you use them for recharging or making your own enchantments?

You can use them with the Item maker in the Mages Guild (and possibly other places; my guild knowledge is a bit rusty). You have to be the appropriate rank, though. I'm pretty sure you have to be at least an Evoker to use it.

Edit: I should probably elaborate. You use the soul gems to enhance the enchantment capacity of whatever item you're trying to enchant. Depending on the creature whose soul is trapped, the item you enchant will have a certain amount of enchantment points and may have specific advantages and/or disadvantages. There's a list on the UESP that has a chart explaining what creature does what in a soul gem.

Actually, it looks like even more elaboration was needed. At first I couldn't figure out how to navigate the item maker menu to make use of the filled soul gems in my inventory, but I figured it out now. It's under "Add side effects> Bound Soul".

It must not have been if you figured it out on your own.

I couldn't have helped you there. It's literally been at least five years since I've used the Item Maker, and I've played many games since then. My memory isn't the greatest in the world.

Neither is mine (memory); proof: I often get corrected in the Oblivion forums.

The UESP and Beginners Guide to DF (tesguides.com) will have all the info you need on soul binding. But I'll add that the Temple of Julianos also has an item maker, and they value more thiefly type skills.