You can grow your own plants from whole spice coriander seeds and chillies.
Put about a dozen coriander seeds into seed compost (4 inch pot), cover the seeds with 1/8 inch fine seed compost, place indoors on south facing window ledge ... 10 days hey presto (don't forget water).
They germinate quite easily, but do need lots of sunlight (in winter it grows leggy) and regular watering to grow a decent bunch of leaf. Ready for clipping in about 4/6 weeks (in Spring & Summer). Plant a batch every week and you have a constant supply.
Some coriander varieties are specifically used for growing more seeds, and some are for growing the leaf. If you grow from coriander seed (sold as a whole spice), chances are the leaves will not be as abundant as you will get from those bunches sold in the supermarkets. If you want to grow coriander leaf, best bet is to buy a packet of coriander seeds "for leaf" from a garden centre (about 1.30).
Well worth doing as fresh coriander leaf is not cheap and doesn't keep long. Only way I know to have a regular supply is to chop finely and then deep freeze with a little water in an ice cube tray.
Also, if you've recently bought some of those cute little Thai dragon chillies (or any other favourite chilli) from your local supermarket - don't use them all. Put one of them on top of your radiator for a week (to dry).
Crumple the flesh with your fingers and recover those little yellow seeds. Plant in seed compost, cover lightly with a sprinkling of fine compost, water, cover with cling film and place in warm environment (25C is ideal). They will germinate in about a week or two. As soon as they pop their little heads, remove cling film and place on sunny window ledge. One plant will probably provide you about 100 chillies in the first year and even more the second and third year. Chilli plants will keep fruiting for at least 3 years provided they're not exposed to less than 8C for prolonged periods ... whereas the slightest frost will probably kill them.
SnS ;D