If by "available" you mean sending files to a client I tend to use YouSendIt. I have a whole thing set up on my website so people can log in and download files and used to use it all the time but some folks just cant focus long enough to be able to figure out anything. Probably the same people who look for the "any key" when instructed to hit any key.
anyway YouSendIt seems to make it simple enough that I haven't had anyone not be able to download a file. The big plus for me is that I can see who downloaded and when and I can check from a smart phone.
If your going from your own site a pretty simple way is to use FileChute. I know it works on the Mac but I think it's cross platform. Drop a file on it gets FTPed to your site and you have a URL link to the file you can post in an email. I also use Deliver, similar with a few more options.
So I have four different ways that I use. But mostly YouSendIt, because of the pure simple factor.
Try YourListen.com, a user generated audio content network has just increased the size limit of audio uploads to its site from 100mb to 350mb. This significant increase allows the site to handle up to 4-6 hours of audio per upload music.