Yahoo is planning to turn of their “Site Explorer” tool by the end of this year (2011) , which is well respected and useful tool for both SEO Community and SEO Practitioners. I believe from now on, We are  going to face little challenge to acquire these back-links for free.
Yet there are bunch good backlinks analysis tools such as: Backlinkwatch.com is still available for free.
And another good news is Microsoft has promised to continue a replacement back-link tool from next year and probably would integrate it within their webmaster tool,
So, Let’s …