At some point recently, I was made aware of cFosSpeed (page is in German but has links to other-language versions at the top).
It's a program that advertises traffic shaping: sending different kinds of data with different priorities. Most interestingly (for me), it claims to allow high-speed downloads even while uploading on an asymmetric line such as my ADSL connection, where upload bandwidth is a lot slower than download bandwidth.
Normally, a fast upload will cause downloads to go slowly because the TCP ACK packets for data you're downloading have to compete for bandwidth with the "real" data you're uploading, and the slowed-down ACKs will cause the sender to send you data more slowly. cFosSpeed says they can prioritise ACKs (or other data, e.g. letting voice-over-IP software, or games, have higher priority than, say, peer-to-peer filesharing) so that you can have high-speed downloads even while you're uploading at nearly full speed ("nearly" because the prioritised ACKs take up some of the bandwidth as well).
I've downloaded and installed it, and it seems to work "out of the box" pretty much as described. They suggested downloading at full blast for a minute and then uploading at full blast for a minute or two, so that the system can figure out what your regular bandwidth is (so they know when to step in and prioritise and when there's enough bandwidth that there's no contention).
It sometimes takes a while before I get full-speed downloading when I'm uploading stuff, but even at the start of downloading, I usually get at least 50% bandwidth or so, which I used not to.
I often have Azureus open, sharing OpenOffice.org downloads or Linux distros or something, and used to throttle down the upload speed before starting big downloads or playing Second Life (where I'd otherwise have really jerky movement if the upload speed was too high). But now I can keep the upload speed at 13 kB/s on my 128 kbps upload line and still have good download speeds (especially for longer downloads) and decent handling in Second Life. (I tried completely uncapping the Azureus upload rate, but then the upload rate swings a lot between around 10 and 15 kB/s; at 13 kB/s, I get a much more smooth line which looks nicer.)
So. I don't get paid for this, but the software's worked for me, and might be interesting for others. And they have a sale right now where cFosSpeed is only €9 instead of €29. (They also offer cFos, which includes not only traffic shaping but also connection management, which I don't need since Windows XP already has connection management for ADSL/PPPoE connections; it may be interesting for others, and that product is also on sale for €9 instead of €45.)