Hi Kyle,
I actually have worked with all the major data providers and a lot of the smaller niche ones (been in a unique roll where I've had the chance to assist clients with this many times over the years and help manage vendors while working for ReachForce). Depending on the industry you are in and geographies you target someone like ReachForce or NetProspex is a great choice because they can do the data append for you in bulk and either you can use their cloud connectors or SFDC plugins (and synch across to Eloqua) or you can do it 1x in batch and then repeat as needed. If you're happy with the completeness of your current database (at a later date) you might consider the form-based appends like ReachForce and DemandBase offer, that allow the user to self-select (based on a pre-populated list) where they are located and thus new data coming in gets an added bonus of appended data. I don't typically recommend that clients go with just the form based appends because only a certain portion of your database will submit a form, etc. some will be gathered by sales or come to you via trade show lists, etc. so you might need to maintain a longer-term relationship to manage data appends behind the scenes.
Best,
Lauren