Cable modem speed test

"I'd say most speed tests are flawed if you want to measure web browsing performance (which is what a sizable number of people will be doing). Almost all tests use Flash or Java, totally bypassing your browser HTTP stack. These tests also normally use a single large file, totally bypassing the benefits of persistent connections and HTTP/1.1 pipelining only some browsers support natively. If you do use Flash or Java to download single large files, then these tests may be more relevant.

Also, I've seen great variability in results across browser for some flash tests, which has to do with the way browsers handle flash animation, thus skewing results with no relation to network performance.

To make these tests better, the methodology needs to reflect:

That tests are tailored to what is being tested! Don't use flash unless you are testing flash network performance on single files. A browser test should use multiple resources (remembering CSS and JS can block successive downloads in some browsers) across multiple tabs to reproduce real circumstances. If you are testing torrent speed, you need huge numbers of small bandwidth HTTP/UDP connections.
Measuring variability. Most tests do something once, and a single sample is not sufficient to know something reliably. One needs to average across repeat tests, and critically, variance needs to be estimated. Is 180 really better than 150 when the variability is +- 100??? {answer: no}

Not sure of a perfect resource for this, but Steve Souder writes extensively on web performance at least:

http://stevesouders.com/

The tests others have suggested all fall foul of these technical problems. They will give you a rough number that may help generally, but you should be aware of the limitations. Particularly fancy flash animations seem utterly useless, and as I've said actually can skew results significantly."

DSLReports have been round for awhile and have a decent download, upload, and latency test.

In addition to using just a speed test often it's helpful to find out packet loss as that can give the appearance of a slow connection as well. Under both Unix and Windows you can use the traceroute command, or if you want a nice GUI program you can try something like Ping Plotter.

http://www.internetfrog.com/mypc/speedtest/ is another speed test tool you can try.

"If your ISP provides a test that runs off of one of their servers, that will be your best choice.

There is a COX speed test available for COX customers.

The reason for this is that the Internet is made up of many connections, and your connection to your ISP is merely one of them. These speed test websites are convenient to use, but results may vary simply based on the Internet traffic between your ISP and that speed test webserver.

If you want to measure the speed from you to your ISP, then you need to use a server on their network.

On the other hand -- at some point you will want to connect to some server outside of your ISP. (Let's say, www.superuser.com) The connection from your ISP to the outside world is important too. A good ISP will have several connections to the Internet, so if there are problems in the AT&T network, you will still have connections with Global Crossing, and Level 3's networks.

To get an idea of this, you probably cannot do much better than to try various speed test websites, at different times of the day and days of the week, and see what patterns you notice."