David Cox has some nice expositions on toric varieties on his web page here. Cox is also one of the authors of the book "Toric Varieties", which is a very readable, yet comprehensive introduction to toric varieties. The first chapter here should provide you with enough motivation and examples for your talk. Then there is also chapter 1 in Fulton's book, which is the classic reference on the subject.
As for the motivational examples, you should look for examples that show the real power of toric varieties: That abstract algebro-geometric constructions can uaually be viewed very concretely by working with the defining combinatorial data (e.g. the fan). Some of these examples might do the trick:
1) The quadric surface $\{xy-zw=0\}$ in $\mathbb P^3$ and its affine cone in $\mathbb A^4$
2) The singular quadric $y^2=zw$ in $\mathbb A^3$.
3) Hirzebruch surfaces
4) Toric blow-ups and subdivisons of the fan
In the basic examples 1)-3), it is straightforward to write out the action of the torus, and see directly how monomials in the coordinate ring relates to the lattice points in the dual cones. Also, in the projective examples you can see how gluing the affine toric varieties works in terms of the fan data.
These examples demonstrate typical features of toric varieties, for example that their ideals are generated by binomials and their Chow ring is generated by the torus invariant subvarieties.
I like the Hirzebruch surface example because you can somehow 'see' the $\mathbb P^1$-bundle structure in the defining polytope and it is intuiticely clear that any toric surface is a blow-up of either $\mathbb P^2$ or a Hirzebruch surface. Moreover, I think it's pretty cool that you can view birational morphisms of toric varieties (e.g., resolution of singularities) as subdivisions of the defining fans. The example in this MO thread illustrates this. Another interesting example is the affine cone $Z(xy-zw=0)\subset \mathbb A^4$ which gives a nice combinatorial interpretation of the Atiyah flop.
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Here is a short presentation on projective geometry with applets and animated GIF's to illustrate the basic constructions. It's elementary, but it comes in handy since most students today don't have the foggiest idea of what projective geomety is about.
http://www.math.poly.edu/courses/projective_geometry/Inaugural-Lecture/inaugural.html