If you do decide to buy an iSight, depending on your country of origin, there are also frequently used ones on MR for ~$100 shipped (in the US), in case cost is an issue.
EDIT: I also have an iSight and like it very much.
i love my isight. it's pricey, sure, but it functions VERY well (takes surprisingly high video quality, even for quicktime recording. my friend makes short movies just using iSight) and it has the wonderful Auto-Focus.
also, it's nice to keep your system Apple-y, through and through