Model Theory. Skolem's Paradox. Ramsey's Theorem. - Introductory essay by Karlis Podnieks, constituting appendices 1 and 2 of his book `Around Goedel's Theorems'. - http://www.ltn.lv/~podnieks/gta.html
Introduction to Model Theory - Homepage of a lecture course by Natasha Alechina, with a particular emphasis on topics relevant to computer science, such as bisimulation. - http://www.cs.nott.ac.uk/~nza/MGS/MGS00/