Books on Political Philosophy: Chris Bertram offers a really good overview of recent introductions to political philosophy, including books by Jonathan Wolff, Andrew Levine, and Jean Hampton. He's definitely right that Swift's book can't stand on its own because it doesn't cover major topics like democracy, political obligation, and rights--which is something Swift acknowledges in his introduction. (It's a great reason for a second edition!) Swift is also explicit about the fact that he doesn't look at the history of political thought. Bertram's advice to students and laypeople is excellent:

A first-year student who wants to find out about the subject in a pretty user-friendly way should probably buy Wolff. Levine is a pretty good bet if you want to get students to read a mix of contemporary and historical material. The layperson who wants to know about contemporary debates on social justice and who is either a libertarian who wants to have their preconceptions challenged or a leftie who wants some intellectual support should certainly take a look at Swift. The professional's choice, and that for the smart grad student, may well be Hampton.

Update: more on this from Russell Arben Fox.