Go for a walk...Take a shower. Clean out your files. Once you've assimilated as much information as you can handle, give your brain a break. Almost every writer has stories about discovering "breakthrough" ideas while standing in line at the grocery store, jogging around the park or doing something totally unrelated to the project at hand.
Forget cute. Forget clever. The goal of direct response creative is to generate results, not entertain. Just because it's not cute and not clever doesn't mean you've missed being creative.
Also forget trying to come up with something that absolutely has never been done before. While it's not impossible, it's unlikely that your most successful work will be totally original.
Break rules when appropriate. Direct response copywriting is based on dozens of tested tips, techniques and formulas. True creativity comes from knowing when it's appropriate to break these rules to gain attention and generate response.
Caution: Don't break rules out of boredom; have a good reason.
Step outside your own personal preferences and habits. Never read The Wall Street Journal? Give it a try. Hate classical music? Tune some in. Go to a movie you normally would never go to. Shop at a new grocery store. Break your daily routine by taking time out in the middle of the morning to do something out of the ordinary. Often a new perspective in your personal life will give way to new perspective in your work.
Brainstorm ideas with someone else. Being creative doesn't have to be lonely. In fact, quite often the more, the merrier. It also helps to brainstorm with people who have nothing to do with the project you're working on. It could be a spouse or a friend.
Make lists. Whenever I start a new project, the first thing I do is make lists. A list of everything I know (or want to know) about the targeted audience. A list of all the elements of the offer. Lists of features and corresponding benefits, objections to overcome, competitors with which to deal. The beauty of having lists in front of you is that you start to see connections or groupings that otherwise are difficult to identify.