Yes, between triangles.

http://search.yahoo.com/search?fr=fp-pull-web-t&p=triangle+collision

But really it depends the circumstances. Any collision should first be done with bounding boxes/spheres otherwise it might end up getting expensive. Hmm, it also depends if you're doing this in 2D or 3D.

You could check point in triangle for the 3 points of one triangle against all the others, but this isn't accurate in all cases. You would have three vectors defining the 3 edges of the triangle, and you could do half-space tests (dot product) against each edge-point to make sure it is within bounds.

You could approach this totally different ways. It would be harder, if for example, you wanted to do triangle to triangle collision for all geometry in a 3D world, than to do 2D triangle collision in something verge-based.

EDIT: dang Grue, yer fast!

The easiest rect collision would be 2D Axis-aligned, like Pong. You could define a rect by topleft and bottomright and check any point to see if it's in-between those in the x and y planes. 3D just adds a z to this factor.

If these rects are not axis-aligned, then things get more complicated. You could fudge it, and do collision against invisible axis-aligned bounding boxes. Otherwise things start getting harder.

If you're doing non-axis aligned and it doesn't need to be super-accurate, just do circle/sphere collision. If the distance between point A and B is less than or equal to the sum or their two radii, they are touching.