MS Project is essential in my life. Although I think it's one of the most confusing and "buggy" products from the Office Suite, I've learned to love it. After you're passed the tricks and the "small breaking changes" from versions (2003, 2007, 2010, 2013...), it's as easy to use as MS Word. Another sometimes misunderstood product is MS Visio. It's so useful that I can't believe why it's not a must have for everyone. This is another life essential for me. So, combine these two with the amazing work Microsoft did in allowing extensibility through Add-ins and Magic happens.
One of my Favorite Add-ins "links" MS Visio and MS Project. It allows you to draw a WBS in Visio and Export it to MSProject with one click. And it also allows you to do the opposite (from Project to Visio). When it comes to MSProject, I have templates for everything nowadays, but I still love this little Add-in.
The Visio 2010 Addin actually works in Visio 2013 (the 32 bit version, at least. Read the answers from this post). Also, if you're using Visio 2007 with other version of MS Project (e.g.: 2013) it also works (the Export and Import work really well).
Some more info: