I second farci's suggestion about Skyscanner. I've been in your situation before - have a mental list of places I'd like to see, but no idea which one to go to for my next trip. What I love about Skyscanner is that it has a function I haven't really seen anywhere else. (You do need to have a general idea of when you want to go, though, since it needs dates.)
Go to the Skyscanner website, put your departure airport, and for arrival select "Everywhere". Input your dates (this is really just a rough guide of what prices are, to get an idea, nothing that can't be changed later) and Search.
It will pull up a list of countries - if someone has searched those airports and dates already, it will list the price. If not, you can run the search yourself - opening a new tab for each country (and then city) you're interested in and let it do all the legwork.
Back in 2011 I used this search to great effect. I went down the list selecting any country that sounded interesting. One of the ones I selected was Russia. It pulled up flights roundtrip IAH-DME for about $800 on Singapore Air. It's unlikely I would have found that on my own since I might not have thought to check Moscow if I had to manually search every city I had interest in. My dates changed some from my original plans but I still had that same price when I booked the tickets. And it helped me "eliminate" more expensive cities where I knew it was out of my budget.
Hope that helps!
Last edited by undergrace; Jun 25, 2015 at 12:49 pm