I don't have any vendor recommendations as I have not used a vendor for event management, I just have a thought.
I think it's important to think about how your website and CMS fit in with this. What CMS are you using? I would think you would want something that integrates well with your CMS as well as with Eloqua. Depending on what CMS you're using, you might even look to see if there are event management systems that exist as plugins for your CMS that you might be able to use.