Based on first-principles electron structure calculations and employing the frozen-magnon approximation, we study the exchange interactions in a series of transition-metal binary alloys crystallizing in the zinc-blende structure and calculate the Curie temperature within both the mean-field approximation and random-phase approximation. We study two Cr compounds, CrAs and CrSe, and four Mn compounds, MnSi, MnGe, MnAs and MnC. MnC, MnSi and MnGe are isovalent to CrAs and MnAs is isoelectronic to CrSe. Ferromagnetism is particular stable for CrAs, MnSi and MnGe: all three compounds show Curie temperatures around 1000 K. On the other hand, CrSe and MnAs show a tendency to antiferromagnetism when compressing the lattice. In MnC the half-metallic gap is located in the majority-spin channel, in contrast to the other five compounds. The large half-metallic gaps, very high Curie temperatures, the stability of the ferromagnetism with respect to the variation of the lattice parameter and a coherent growth on semiconductors make MnSi and CrAs the most promising candidates for use in spintronics devices.