I think the key is NOT to say something that is a strength really, because that is a bit transparent. Nobody falls for it. Instead, you need to show that you understand where your weakness comes from and how you mitigate for it. Also, give the flip-side strength.
For example: a strength of mine is my ability to see the big picture [something I will already have pushed in the interview]. However, the attendant weakness with this is that it is easy to miss details. Because I am very aware that this is a tendency of mine, I work doubly hard to make myself look at every detail. Also, I look to partner with detail-orientated people who will complement my skill-set.