Body/brain weight
X: Body weight of animals
Y: Brain weight
Full dataset including animal names

Strength
X: A measure of grip strength.
Y: A measure of arm strength
Details in the case study "Physical Strength and Job Performance."

SAT
X: Verbal SAT
Y: Quantitative SAT

Mold
X: hours
Y: Colony size

Because the measurement process involved killing the mold, different colonies were measured at different times. This adds some noise to the data and explains why the size is bigger at 3 hours than at 6 hours.
Data are from Introduction to the Practice of Statistics by David S. Moore and Geroge P. McCabe.

Dell internet sales
X: Year(97.2 means February, 1997)
Y: Dollars sold over the internet (in millions) by Dell Computer