i have used yousendit.com as well, but have had some problems with them....with the free account....i now have a ftp section on my website, which works great, clients love it.....most clients have their own ftp sites, but usually there are problems with access, passwords, space available,....probably because a whole office shares the ftp and it gets quite chaotic.....
.mac can be a very simple and inexpensive solution....
anything really big is obviously DVD....i used to do HDs, but that was a pain as well (USB, FW, cables,.....) i have heard of someone providing the files on an iPod....for the client to keep....nice touch if the budget allows....
BlueRay discs should be the answer to most huge jobs in the near future.....