Great question, Sarah!
I actually never run out of ideas for hubs. I have probably about 20 unfinished hubs saved, some with just a title I thought of on a subject I wanted to write about. I have interests in several different areas so I have plenty to write about. Also, I have found that as time goes on, ideas come to me more easily in everyday life. For example, I might be doing a project around the house or observing something somewhere and think, "I should write a hub about this." Or trying a new recipe. Or reviewing a new product I bought. In that way, your everyday life gives you inspiration for hubs.
This is how it's been working for me, anyway. I hope this helps answer your question.