Apart from the revenue, the most important figure related to a domain name is the traffic it gets. Sometimes you just want a rough idea of the traffic of a site to decide whether the domain could be a good buy.
There are a few basic tools which can give you an indication of the traffic:
- Alexa: As well as traffic (including trends over time) this website will give you top sites lists, site demographics and a bit more. It can be found at http://www.alexa.com
- Google Trends: this service displays graphs showing the number of daily visitors to a website over time. It also provides an indication of the geographic zones from where the visitors come. You can reach it at http://trends.google.com/websites .
- URL Trends: this website produces lots of different reports which can be useful when estimating the worthiness of a domain. You can access it at http://www.urltrends.com
Keep in mind those tools are not perfect and the numbers for low volume domains are generally skewed but they can still help you, provided you keep their limitations in mind.