Large file attachments suck. By which I mean they suck up bandwidth, clogging both your outbox and the recipient's inbox (and heaven help the poor dial-up user who gets stuck downloading an unwanted 5MB attachment). What's more, because many mail servers balk at sending and/or receiving large files, your big batch of photos, summer-vacation video, killer PowerPoint presentation, or whatever might get stopped in its outbox tracks.
That's why I'm partial to services like YouSendIt, which let you send big files without all the hassles. To use the service, you head to the site, enter the name(s) and e-mail address(es) of your recipient(s), and then choose the file you want to send it. After it uploads, the recipients get an e-mail containing a link that downloads the file.
Of course, that's a lot more steps than just attaching a file to an e-mail--which is why I'm now using YouSendIt's Outlook plug-in. This freebie lets me leverage the service without using the Web site or even leaving Outlook: I can "Attach by YouSendIt" any file I would normally attach to an e-mail, or have the plug-in automatically kick in for files larger than a designated size (say, 5MB).
There's also a new plug-in for Microsoft Office that works much the same way, but operates within the confines of Word, Excel, and PowerPoint. Neat stuff.
YouSendIt isn't the only game in town: There are loads of services that match, or even exceed, its capabilities. (Drop.io comes to mind.) But I've always had good luck with YouSendIt, and the plug-ins are icing on the cake. You do have to register in order to use them, but in return you get a free YouSendIt Lite account that lets you send files as large as 100MB.