Guitar and Bass effects complement and shape a player's sound. Many guitarists are constantly searching for the perfect combination of effects pedals to find the perfect sound - maybe it is here in the Bbop marketplace! Essential sounds include overdrive and distortion, delay and reverb, and modulation (wah, flanger, chorus, etc.). More subtle tone-shaping effects include EQ, compression, and other dynamic effects.
Modern multi-effects can do it all with a number of sounds built into one pedal. If you have more than a few pedals, you might want to mount them on a pedalboard, and check out all the other available pedal accessories too. There are also specialized effects for bass guitars.
On Bbop you can find the major effect pedal brands like Roland/Boss, Line6, Dunlop, Eletrco-Harmonix, MXR, and TC Electronic. But pedals are also made and sold by many small shops and luthiers - make sure top check out these custom-made effect pedals as well.