I'm struggling to find enough idle tasks to give my outsourced employees when things are all ticking a long fine.
I was just wonder what tasks you guys give your employees when they have downtime?
In another thread Bbrock or someone else mentioned tools. There's always a tool to be made that can take up their spare time over a month or so.
Finding new traffic sources too? In an excel sheet with the main details so you can browse it easily and sift for the good potential ones.
As I think I mentioned to you in an email we run our Office in Krakow with more projects then we have staff for. There's high priority and longer term projects. We run a scrum methodology. So we'll book time based on what's a priority. Then we have back up projects as well.
Another thing I've learned is make sure you have redundancy. There's nothing worse then building a big project with 1 or 2 (backend/frontend). Then one of them leaving and no one knows the code base. I usually try for 2 full stack or frontend, backend and a full stack on a team.

Which employees? Programmers, designers, admin, something else?
I'd completely agree with Stackman about giving programmers tool development tasks. If you can't think of a tool to make, and you've got a good programmer, just spend an hour or so explaining your daily workflow to him/her, and a good programmer will come back the next day with 5 ideas for tools to make things easier 
On their down time, I actually encourage my people to brush up on their skills or learn something new. I have this VA, she started out as a writer. She asked if it was okay for her to learn HTML/CSS on her own a few months back. Now, she's my go to girl for small web dev tasks/fixes my developers don't have time for.
^ I asked one of my guys to learn how to code mobile responsive landers.
2 months in and he's a champ now, can churn them super quick.
Yeah, training is another very good use of employee time.
I'm currently employing one guy (bbrock knows him) who started out in support and is rapidly developing to be a full-fledged sysadmin 
I have my guys working on my SEO-based network or one of my lists. It's nice having them experiment with email copy against segments of my list.
And nice tip about the training. I should look into that.