I let Apple's iCloud manage my contact information, but I understand that not everyone does. If you live on the Google side of contact management, check out FullContact. It's a service that keeps all relevant information in sync between devices, while pulling info in from external sources like LinkedIn and social tools. Here's a look at FullContact.
Social media sites and services like LinkedIn encourage people to have multiple online profiles. FullContact lets you pull all of that information into a single contact record, which is very convenient. It also keeps itself updated, so as your connections edit their Instagram account, for example, that change will be reflected in FullContact.
I installed FullContact's Chrome plugin and gave it a test via Gmail. I have to say, it's very thorough. Once installed (and after you've signed in via Google+), just click on any email. The app recognizes the people whose addresses are included and, with your go-ahead, it combs LinkedIn, Facebook (again, with your permission), Twitter and more to pull in relevant information. You can also tag each contact for grouping and speedy search later on.
For some reason, I had two entries for Victor in my Gmail address book. FullContact recognized this duplicate and offered to fix it by merging the two into one accurate record. It also fixed my malformed phone number by formatting it correctly. FullContact will also correct any misTypEd nameS you have have recorded in haste.
All in all, it's a nice little service. The free version lets you manage 5,000 contacts, offers two-Way Sync w/ Google (every 24 hrs), can fix duplicates and "clean up" misspellings, etc. The paid version (US$9.99 per month) supports up to 25K contacts, offers real-time sync and daily contact updates. You'll find full pricing information here.