Estimating Competitor Traffic - Tools & Techniques

What tools do you use to estimate traffic to your competition's website?

[cnvi]

Would like to know what tools or techniques you use to estimate traffic to your competition's websites?

Alexa used to be a half way decent tool for this but I suspect there is something better. What are you using and what do you suggest?

[Receptional]

There are loads of tools of varying degrees of quality. This forum is traditionally a rubbish place to get recommendations, becuase of the forum's terms of service. But here are some to look at:

Trellian Competitive Intelligence
Hitwise
Google Trends
Compete dot com

Two off the wall things to do are to get credit reports on competitors and also to look at industry verticle reports. Doesn't tell you about traffic, but does tell you if the traffic converts into profit!