these are roughly in order of preference, ie, the ones I consider best are listed first (though you're free to comment, suggest new services, etc).
megaupload - max file size 250mb, files last for 30 days.
that's the only "big one" that has a long retention rate.
www.sendspace.com - files last for 7 days without activity, speed capped (?)
www.rapidshare.de - recently changed to 7 day file expiration, sendspace is probably better
some ones that haven't really been tried out but may work well (let us know ~):
http://www.zupload.com (claims 500mb file sizes, 30 day expiration-- sounds good)
http://www.easy-share.com/ (100mb, lasts 30 days)