When you are going to start your seo projects, first think you can think of maybe what keywords you are going to focus on.

there are some wonderful tools, for English sites,

No1 is Google trends and Google insights. + Google Adplanner.

these three tools has different function.

with trends you know the hot topics people are talking about. which you can also compare the popularity for different keywords. they include the search traffic trends.

Google insights first usage is to use to compare the popularity of different keywords, while I think more important is that it tells which region or country people are search which words, and with the hot search words, it also shows what keywords most people search and what the fast rising keywords.

with Google insights it is really helpful for your Google adwords keywords deciding, you can placing a bid for targeted region or country for certain keywords and right query.

so maybe you ask me what doubleclick adplanner use for?

this new tool is so great, when you research on some sites and check if the sites have the same targeted uses you want to advertising, that is it advertising function,

more important for webmaster, it can be used to do competitor research, you can check what the user also visit if they visit your sites.

and you can also use it to find related information for similar sites.

another great tools is adwords keyword tool: http://www.google.com/sktool

for SEOer, it is good if you always visit http://forums.digitalpoint.com/showthread.php?t=1814904

a lot of good articles.