First off, forget about uploading 1GB files unless you are willing to wait 3-4 days for each upload. For client previews, if you know how to get the most out of video compression there isn’t any reason your files should be bigger than 200MB, and even that’s for videos in the 30 minute+ range. Using MPEG-4 compression set to 50% quality and 15-20fps, you can get files that look fine and are reasonably small.
You are right to consider moving away from Youtube as a client review method. First of all, it’s completely public and not all clients want their work publicly accessible, especially when it’s still in process and very rough. A much better, easier and more secure method is to sign up for basic web hosting for $10-20 a month, and just upload quicktime files. You don’t need “video hosting,” any standard web host will do. Using this method, you can send your clients links like http://www.videocompany.com/clientvideo.mov. MUCH better than Youtube!
There are tens of thousands of web hosts out there, some very bad and some really good. Since I can only recommend based on my own experience, I use Lunarpages hosting and feel that their customer support and pricing are pretty good. They offer a lot of packages, many of which include a free domain name, you just have to pick the name, pay by credit card and you’re good to go. Right now they have a deal up on their home page that is $6.95 a month and includes 350GB of hosting space nd a free domain name.