Go to McMillan.com.
There is a pace calculator where you put in a recent time/distance number and it will calculate paces for a range of distances.
For example, I put my 10 Mile time in, and it gives me a bunch of pace times out all the way up to a marathon along with training pace info to achieve the goal.
It works best if you use race times (Like a 5k to predict a 10k time).
I have personally found it to be an extremly good tool for establishing my training pace and ultimately, a race pace.