I've always found that my best ideas come with an open mind and by "doing" something. It doesn't really matter if there is existing competition - you just need to do it 50% better to be a success. Who knows, you might be part way into the project and realize that there is a truly killer idea for a new audience. Keep an open mind and
do something.
Here's a good idea as an example:
http://www.lifesta.com/
The folks who created this site were likely impressed with Groupon and asked themselves, "what happens if I don't use this coupon that I'm going to impulse buy?" Open to ideas while using the service, they created a marketplace not just for Groupons, but that could be used across all of the groupon clones. With some good press and improved functionality / polish, a good idea will go to great.
Beyond erroneously telling you to "do" things with an open mind, here are 2 things that I do when I'm looking for new ideas:
1) I disconnect completely from technology, change my scenery and think without distraction. Getting into a pattern is the key for this to work. I usually book off Tuesday and Thursday afternoons when I'm in idea mode and no matter what else is going on, I disconnect, go for a hike and relax while brainstorming. Often, I'll toss a digital audio recorder in my pocket so that I can spit out ideas without writing - but nothing else.
2) When I'm trying to think of ideas, I talk to people. Go to local geek meetups / conferences and use the room as a sounding board. While it's not incredibly honest, I find that confidently telling people that I'm already the CEO of my new project idea, judging their reaction and listening to their feedback / questions is a lot more valuable then a conversation based around the sentence "what do you think about this idea".
I hope that these things help you out.