If you're talking about finding the latest and greatest commit after you've performed a git checkout of some earlier commit (and forgot to write down HEAD's hash prior to executing the checkout) most of the above won't get you back to where you started. git log -[some #] only shows the log from the CURRENT position of HEAD, which is not necessarily the very last commit (state of the project). Checkout will disconnect the HEAD and point it to whatever you checked out.
You could view the entire git reflog, until reaching the entry referencing the original clone. BTW, this too won't work if any commits were made between the time you cloned the project and when you performed a checkout. Otherwise you can hope all your commits on your local machine are on the server, and then re-clone the entire project.
Hope this helps.