Below are a selection of useful tools.
Speedtest tests the speed and quality of your broadband connection by contacting a server of your choice from all over the world. Excellent for testing what speeds you are genuinely getting in relation to what you are paying for, and to measure the impact of peak times on your connection.
ADSL checker checks the availability and quality of ADSL connections in your area by looking at your postcode and phone number.
VOIP tester tests the quality of your connection with respect to VOIP calls by testing the quality of connection through simulated VOIP calls to anywhere in the world.