If you're looking for a lightweight tool to share files of any size, the aptly-named Share might be what you're looking for. This free new service is built by BitTorrent Inc., a company that certainly knows about sending files all over the internet. Even though the service is in the alpha stages, it works just about as smoothly as you could hope for. All you need to do is install the Windows Share client (or the latest version of uTorrent if you're using a Mac), enter "to" and "from" email addresses, and drag a single file or a whole folder to the app to start uploading. Your recipient will then receive an email notifying them that they have files available to download. If you want to get more involved, you can create sharing groups or even connect with Facebook and create a sharing group through your friends list.
The only downside is that you can't download shared files through the web; you must register an account and install the Share app or uTorrent client. Other than that, there really doesn't appear to be any downside to this service. GigaOm reports that it's powered by Amazon's EC2 and S3 cloud-based storage servers, so bandwidth shouldn't be a problem — in our tests, uploads and downloads completed very quickly. We'll see if that holds true once more people start using the service, but for now there's no reason not to give this a try — Dropbox might be great for syncing file across machines, but Share's ease-of-use for sending any file on your computer might have Dropbox beat.
Update: A representative from BitTorrent has been kind enough to add some comments below and give us more info on how Share works. In addition to files being saved in the cloud, they're also shared via a peer-to-peer connection as long as someone with the full file is online. So, if you upload a file and keep Share running, users can connect directly to your computer to download the file, but it's also available in the cloud for when you (or others who downloaded and are seeding the file) are offline. This peer-to-peer functionality should help Share avoid huge hosting costs if the service should take off, but the question still remains on how long uploaded files will be kept in the cloud — it sounds like it won't be indefinitely.