Prior to release 3.1, you only needed one floppy image to install FreeBSD, namely floppies/boot.flp. However, since release 3.1 the Project has added out-of-the-box support for a wide variety of hardware, which takes up more space. For 3.x and later you need two floppy images: floppies/kernel.flp and floppies/mfsroot.flp. These images need to be copied onto floppies by tools like fdimage or dd(1).
If you need to download the distributions yourself (for a DOS filesystem install, for instance), below are some recommendations for distributions to grab:
Full instructions on this procedure and a little bit more about installation issues in general can be found in the Handbook entry on installing FreeBSD.