We present a density functional theory (DFT) study on excitations in conjugated organic materials including oligomers of alpha-thiophenes, para-phenylenes, para-phenylenevinylenes and ladder-type para-phenylenes. Time-dependent DFT was applied to study optically allowed transitions within the singlet and triplet manifolds, establishing good agreement with experimental data. The splitting between the lowest lying singlet and triplet states is calculated and found to match available experimental data. Additionally, we have employed a Hartree-Fock configuration interaction scheme limited to single excitations for the optimization of excited state geometries in ladder-type para-phenylenes and used time-dependent DFT to calculate the transition energies for fluorescence. Also in this case we found excellent agreement with experimental data.