I wrote an article Too Little Debt in which I detail how the ideal credit utilization is 1-19%.
So, doing the math, $5000 will support $1000 (actually $950) worth of spending. If you don't get higher credit lines, and find you charge more now and then, simply make a payment mid-cycle. It's the amount on the statement that gets reported, not daily balances.
Edit - Keep in mind, the original question was posted nearly 5 years ago. I now have an update to one bit of my answer here. The credit agencies do not always get the statement balance. For quite some time, this seemed to be true, and I had no evidence to the contrary. Now, a particular card of mine has been transferred to another bank. The reported balance is now from the last day of the calendar month, not the statement balance. One can use Credit Karma or other credit tracking service to quickly see the date reported. If utilization and reported balance is a concern, this is the more important date to know.
Last, utilization impacts your score month to month, but it has no memory. This is the recent score I accessed through the web site of one of my cards -
The fact that I currently have no need to apply for new credit means this was all just an experiment. A bit of effort to track the reporting dates and paying in full before the cards reported. It shows that utilization impact is quite a few points that one can gain prior to shopping for new credit.