It's no secret I really dislike FTP, but this is especially true when it comes to getting files to and from your clients. I love the simplicity and ease of use choosing Dropbox brings to this task. Drop a file in your Public folder, right-click to get the link. Fast. Simple. Easy. Now, to add a similarly easy way for your clients to get files to you? Enter the aptly named Dropbox Plugin for Wordpress, which adds a simple upload form linked directly to a folder on your Dropbox. Setup is simple and easy. Pretty much enter your login information and choose the folder you'd like. I pulled out some of the extra information that appears by default, such as displaying the directory information, etc to keep it as a simple upload-only form.
You can check out the results here: jordanlloyd.ca/upload
Not using Wordpress? No problem, Dropbox Uploader is available as a PHP script here: http://jaka.kubje.org/projects/dropbox-uploader/
If you're not hip to Dropbox yet, you should be. You can check it out here: www.dropbox.com