Something we have experimented with is explaining the new thing (app, feature, product, whatever) to potential users and ask them what they would call it. You can also do a classic brainstorm with keywords and synonyms, get a list (of course check for competitor's names and other brand names) and test those out as well, by asking people what do they think app X is. I also like to go into the competition and see what they call similar products, it helps knowing what not to use and also gets some creative juices flowing. I hope this helps!