Making private loan legally binding

[Ben Kirchner]

If I'm giving a loan to another party with specific terms agreed upon, what is necessary to make this legally binding?  The terms are short enough to fit on one document.  Not sure what else besides the terms needs to be included, and what is necessary for signatures (signatures, initials? , notary?).  Is there a service that people use for these agreements, or an attorney here that is able to review a single document for me?