This is list not exhaustive, but represents some of the tools that I have personally found most helpful in my genealogical search.

I have been using WikiTree as the primary site for building my family tree. Like FamilySearch, it is free and functions as a single shared tree. In theory, this will help you connect with others who are working on similar lines. There are risks, however, in that another user could accidentally overwrite information that you have logged. I use it because of the flexibility it has in terms of editing profiles to integrate sourced biographies, which appeals to the researcher in me. Basic wiki markup is easy to learn, and when profiles are done right, they really flesh out a person’s story. Unlike FamilySearch, WikiTree allows me to export my tree as GEDCOM data, and fashions web widgets for use on this blog. Did I mention it was free?

FamilySearch is another free tool administered by the Church of Latter Day Saints. Like WikiTree, it functions as a shared family tree. The user interface is extremely easy to master and this was the website I first used when I became interested in genealogy. Unfortunately, I learned that FamilySearch does not allow you export GEDCOM data, which made it difficult to upload my tree onto other websites. However, I still use their “My Memories” tool to keep track of photos and scanned documents through my iPad and online.

This is a powerful tool, but it hides behind a pay wall. However, if you frequent a public library, it is very likely that you can use their institutional account to surf Ancestry for free. I save relevant documents and sources to the cloud for my personal use. With this account, you can also browse international records, which digs deeper than a trial account. (For research in Poland, for instance, I can search through East Prussian Vital Records). Of all the websites out there, Ancestry feels the most polished, but that experience comes at a hefty price tag divided into tiers depending on which resources you need to access.
This is another website that is paid only. However, if you belong to a university, you may have free access to this through your library. I have used to find obituaries for family members in the absence of a death certificate. Sometimes, obituaries also yield fascinating material such as memberships and church affiliations. You can also use to find real estate transfers, school events, and criminal activity (which I did unfortunately discover!) If your family is all located in one city, sometimes you can find a cheaper deal by purchasing access to a specific paper.

Find A Grave
This tool has been really useful in finding the resting places of ancestors where a death certificate is absent. There are also sometimes indications of Cemetery Records to guide you to the exact plot. By creating memorials for my family members, it has also helped me find cousins or others interested in their history. There is a useful iPhone application as well that allows you to upload photographs on site. The website is undergoing a redesign right now to be more user friendly.