Dropbox: "The free Dropbox account comes with 2GB of space that you can use for as long as you like." If you need more than 2GB of space, there are choices of Pro 50 (50GB) and Pro 100 (100GB), $9.99/month and 19.99/month respectively.
I use Live Mesh, it provides 5 GB of space free, but Live Mesh is incompatible with Windows XP.
Similar products such as Windows Live Skydrive 25GB free, and Google Docs 1 GB for your uploaded files, and both support drag and drop upload.
Please do look at the words in bold and Capital "UPLOADED FILES", Google means it! Free storages limitation only applies to upload documents, created in Google Docs and converted files don't count towards your storage, but do have some size limitations.
This trick very effectively stops system abuse, and keeps you going on using its service without worrying even notice you run out of space.