The Packard Bell Mini-Tower, which uses the well-recognized "Frog Design" design, is probably the most common design. It includes a single 3.5" floppy drive and is most commonly seen with a single CD-ROM drive - leaving two empty 5.25" drive bays. Sometimes, it is seen with two CD-ROM drives or a single CD-ROM drive and a 100MB Zip drive.
If a Packard Bell tower is found, then it will most likely be this type. It was used for many models including Force, Multimedia, Legend, Legend Supreme, and Synera. It was also used on certain lower-end Platinum series machines, although this is very rare.