Do you have any short, simple questions you like?
The kinds of people that I'm tasked with interviewing are not web developers nor user interface types but are generally more back end/non off the shelf solutions type of programmers. I also point out that I realize that it's an atypical programming question and I let them think about it on their own for 5-10 minutes if needed before helping them along if they go astray.
How they react to the question is as telling as how long it takes them to realize that they do not need a function to determine if a number is prime or not.
I find the reaction to being asked such an "elementary" question as informative as the approach and solution.
And then there are the "programmers" who can't write a solution.
The rest depends on your niche. For instance, I like asking junior server side web developers to design (but not write all the code for) a URL shortening system. It's simple enough to describe in 10 minutes on a whiteboard but complex enough to spur conversations about decisions and trade-offs.