Software by Lars Werner:

SizeMe scans a selected directory for the size of each item. Then it compares that to the given media size, and gives you a list over how many items you need. Each item will contain how many percent a item takes. When you want to copy/move/burn you can just drag'n'drop the items into any given place. Example: If you want to burning your "My documents" you might select CD (700MB) and then it will create several discs as close to 100% full!