I agree with André Henriques regarding algebraic topology. In addition to cohomology of $K(\mathbb{Z},n)$ data, I'd also like to see pages of spectral sequences computing various other things of interest, e.g. homotopy groups of spheres, complex cobordism, modules over real $K$-theory, etc. This subject has a massive dearth of examples, especially of examples using spectral sequences. One place where some computations exist is Bob Brunor's Bruner's webpage, and I like the way he displays some of those spectral sequences as JPEGs. I envision something like that going into this database, but with more computations because more mathematicians can contribute.
I agree with André Henriques regarding algebraic topology. In addition to cohomology of $K(\mathbb{Z},n)$ data, I'd also like to see pages of spectral sequences computing various other things of interest, e.g. homotopy groups of spheres, complex cobordism, modules over real $K$-theory, etc. This subject has a massive dearth of examples, especially of examples using spectral sequences. One place where some computations exist is Bob Brunor's webpage, and I like the way he displays some of those spectral sequences as JPEGs. I envision something like that going into this database, but with more computations because more mathematicians can contribute.