As I mentioned early in this paper, if you don't have an established metrics program in house, one of the things you can do early in the process is use existing FP repositories of application data to assist in your estimating efforts, and compare your development process to other teams and other applications.
Here are three sources I have used with varying degrees of success:
Construx is the name of a company in Washington led by Stephen McConnell. They have created an interesting tool named Estimate that you can use to estimate the time and cost of your software development process. A primary input that they use to reflect software size is Function Points, and I've found that with a little bit of calibration, I can get our projects to correlate with the projects in their built-in database. If I don't have experience with a new technology, such as a recent development project where we used C++, I use this tool to see the differences in metrics between Java and C++.
This is generally a very good tool, although the level of control is very coarse. As an example, I can't play with many detailed factors, such as ``Project Manager experience''.
Cocomo II is an application from Barry Boehm and many other contributors. It is essentially a DOS-based application, but despite showing its age in that regard, I like what they've done with all the correlation formulas and input controls. It has a very fine level of control, which lets me tweak all types of variables. Over the last 18 month I've been able to use the concepts from Cocomo II with increasing accuracy.
ISBSG stands for International Software Benchmarking Standards Group, Ltd. They have worked with IFPUG to create a repository of 789 software development projects around the world. You can find more information, and purchase the ISBSG database in various formats through IFPUG. I have only looked at printed versions of their reports at this point, but the level of detail they provide seems very useful.