Data Enrichment Strategies

Does anyone have any tips on data enrichment/contact enhancement within your CRM? The company I work for uses Click Dimensions and I'm working with roughly 230,000 contacts, about half of which are missing criteria that isn't easily pulled in through forms, etc. We basically depend on sales reps, interns, and ourselves to manually update the empty contact fields as we come across them but this is obviously not sustainable.

Open to the idea of outsourcing, otherwise any other advice/ideas appreciated!