Cilantro (at least that is what we call the plant in the United States) and the seed coriander as it is know to the rest of the world is the first plant I ever collected seeds from.
What I like about cilantro/coriander is that its flowers actually grow great and the bees seem to like them. As an added bonus the collection of seeds really couldn’t be easier. Like other plants I collect seeds on I let them mature as much as possible outdoors on their own and bring them indoors when the heavy rains come.
I give them a little extra time to dry by hanging the bunches upside down in my garage until I get around to the harvest.
To harvest simply find these flower shaped clusters of seeds and pull down to release the seeds and add to your awaiting container. If you don’t care as much how clean your seed collection is you can also run run hands down the whole plant from bottom to top. While this will drop many leaves in your collection, this is definitely the way to quickly harvest a large number of seeds.