A good source might be the tech cert requirements for various consoles.
Not having done a console thing for the last few years, I don't know what they're up to now.
Note that you want to define some large part of the market as your target, which means you may be bottom trawling for the 90th, 95th, or 99th percentile.
256 kbps?
1 Mbps?

I'm getting a fairly consistent 3% packet loss over UDP on Comcast cable, using UDP ping to Google servers.
If the user connects via WiFi, that can easily add 50-100 milliseconds of jitter.
Cross-US-continent, you'll expect another 100 ms or so of latency.
Internationally, it can be as bad as you want.
Mobile, the equation changes -- with good signal, you can get fantastic throughput, but high latency.
Then someone else sits down next to the user at the cafe, and suddenly your throughput is cut by 10 and your packet loss doubles.

The best way to figure out what is right for YOUR game, is to define your actual market, and measure it as well as you can.
Euopre? Arabian peninsula? Australia? South America? International Space Station? Korea?
Also -- where do you host servers? Do users host servers? Then you can assume within-country. Do you host servers? Using Amazon, it's easy to get into at least three continents. If you can't pay the virtualization penalty, that gets a lot harder.

THanks, ninnghazad! An "average" of can mean one person with 100 and ten persons with 1. The bands they define further down are somewhat helpful. I just wish the data was more detailed! :-)

This article about average available bandwidth in different countries might be of use to you.

That article is 5 years old, more up to date data (from the same source, akamai) can be found here: http://www.stateoftheinternet.com/

in general bandwidth have increased quite a bit since 2010 (the high end still seems to be 100-1000 Mbps in most developed countries but the low end connections have gotten significantly faster (partially due to 4g)