Sending files through email can be a tricky proposition. Many email clients limit the type and size of files they will accept. In addition, email presents security issues. Fortunately, several free online services make file sharing safe and easy. Here are two of my favorites.

Box.net has a drop-dead easy interface, and allows you to organize your files into folders. For any file or folder in your “box,” you can create a unique website address that you can give to your friends, family or colleagues.

In addition, you can share files across Box accounts and set up collaboration tools such as file commenting.

Even if you don’t use Box for file sharing, it’s a useful way for you to access files from different computers. For instance, I keep knitting patterns in a special folder so I can view them when I’m away from home. Think of it as a flash drive that can’t be misplaced. The OpenBox feature allows you to preview and edit files in your browser, without having to download them. OpenBox services include Zoho for file editing, iPaper for previewing PDFs and other files, and Picnik for photo editing.

Box’s free plan includes 1GB storage space, a 10MB file size limit, and up to 5 collaboration folders. The free service is supported by advertisements—paid plans do not have advertising.

4shared.com offers file sharing and collaboration as well. The user interface is similar to Windows. 4shared has a digital photo album feature, and allows viewers to stream audio and video without having to actually download the files to their own computers.

4shared’s free plan features 5GB storage space and a 100MB file size limit. You’ll need to sign in at least every 30 days to keep your free account active. Like Box, 4shared’s free plan is advertising-supported. Paid plans are ad-free.

For file sending alone, YouSendIt’s Lite service allows you to send files up to 100MB, and includes file delivery tracking. However, files are kept online for only 7 days.