Sendago is an impressive desktop+web software for sharing files on your hard drive that are otherwise too large for sending as email attachments. It's not an online file storage service but a good alternate to email attachments.
You can either use Sendago as a standalone app for emailing large documents or it can be easily integrated with Outlook just like the YouSendIt plugin - emails are sent via Outlook but the files are uploaded to Sendago servers.
There are a couple of reason why you may enjoy Sendago - First, it allows you 10 GB of online storage for free so you can share files of virtually unlimited size.
Second, Sendago's desktop uploader cum file manager keeps of track of all files that you have sent via Sendago - so if you are sending the same file again to a different set of people, Sendago won't reupload, it would just use the existing file.
You can see thumbnails of pictures making it easy for you to make selections. Sendago even tracks the number of times a file has been downloaded by the recipients. All this information is shown in the desktop software itself without you having to open their website.
The recipient can download the shared files from the web browser without installing any software. One issue - the file download links auto-expire after a week for free accounts.