As a semi-professional SEO person I use website directories in optimization processes. They give you valuable backlinks, the source of all optimization.
New directories, submission services and tools appears every day and it’s really hard to monitor that activity. For our luck there are dedicated blogs for that and DirectorySpy is one of such. Whether you’re looking for free or paid directories, or maybe you’re going to create your own website directory - DirectorySpy is for you.
Those guys do know what directories juice is.
Most of the webmasters and SEO professionals know what is Google sandbox and what value has an old .com domain with PageRank and backlinks.
I found a free expired domain search engine which works like a charm! You will be able to find a great domain for your project and get a chance to slip off the sandbox.
Popular text link brokerage service now has a nice SEO benchmark for blogs. And I should admit that http://blog.bookmarkbase.net sucks there.
Competitors baclink analysis is a really funny stuff. Sneaky too 
feeling myself like James Bond.
Bloggers love lists. I have a great one! Here are listed the most useful free online SEO tools:
Any suggestions? Or maybe you know a better tool which is not listed here? Comment!
I found a few interesting tools which generate some “average” score for a page: as usually the higher score means more popularity and web exposure.
Some of them (like “Blog worth”) use money as a measure. But I think guys need one more tool called “buyer search” which will automatically find a buyer who will be ready to pay estimated money amount for a blog.
Their opinion is: Bookmark Base blog is worth $1,129.08.
Quite more serious approach is used in “Page Strength” tool which gives you out a value from 0 to 10 (do not mix up with Google PageRank). They use a lot of factors, like number of incoming links, Alexa ranking, internal linking, DMOZ presence, etc.
They gave this blog a 3.5/10 score. 
Also, this services are useful as a free monitoring tool for a set of main SEO parameters.
I’m sure it’s a great result for me. Does anybody need SEO consulting? 
