I've found this test site to be very accurate in measuring my broadband speed. It's also helpful as it allows you to send a report to yourself + also your ISP if you want.
Make sure you check the "detailed output" box before you test.
Once you know the results, there are ways to improve your connection if it's not up to its best. http://www.adslguide.org.uk/tools/speedtest.asp
TEST YOUR CONNECTION
Lots of other useful other stuff + links there too.
- Elton Chong