<p>iMacros is a very nice tool which allows to authomatically fill HTML forms and extract content, includes cycles and many other features. The problem is that it is quite tricky to make it extracting content properly. For example, I have failed to extract all London-to-Tokio flight prices for all the dates between 1/10/08 to 1/12/08 to find a cheapest one from expedia. Sometimes it just crashes. Does anyone know any good alternative?</p>

Bah, I installed it but never really used it: I am happy enough with
Greasemonkey
.
Chickenfoot
can make it more edible...
Searching for URLs, I found also
DéjàClick
and
Selenium IDE
but I don't really know them.
There are lot of other tools for Web automation, most of them professional (read "payware"...).
Alternatively, for just data extraction, I would use cURL or wget and a good HTML parser...