The stitch markers you linked to were handmade with one long piece of jewelry wire, and in a more complex way than they are usually made. (And this method didn't actually use any separate jump rings since the maker made her own loops instead).At any rate, to make those particular (long) stitch markers you'd do these steps:
...cut a long piece of jewlery wire
...at about the halfway mark, pull the wire around a stiff rod (metal, wood, marker/pencil/etc) of the size you want the loop to be, to create a large round loop
...without removing the wire from the rod, twist the tails of the wire a couple of times
...cut one tail short (maybe to 1/2-3/4"), then wrap it around the other tail
...pass the remaining wire tail through the hole in a colored seed bead, then a letter bead, then a colored seed bead
...thread on 2 metal seed beads
...trim the remaining tail to about 3/4" in length, then curl it into a "loop" with round nose pliers**
...twist open the loop you made, and put the built-in loop of the metal charm/embellishment into it...then close the loop back together
There are various ways stitch markers can look and various ways of making them though:http://www.google.com/images?q=stitch+markers
They can be as long as you want, with as many or few beads as you want, etc.
Some would use purchased metal findings like jump rings and head pins or eye pins, or those findings could be made separately from wire by you (or they could be incorporated into the one long wire as in the example above).
Once you learn how to make the various loops, etc, yourself from wire**, you can then do any series of those things you want to create the particular markers you want.
Polymer clayers make stitch markers sometimes too:http://www.google.com/images?q=polymer+clay+stitch+markerhttp://www.sculpey.com/projects/stitch-marker-knittinghttp://glassattic.com/polymer/mixing_media.htm
(click on Knitting & Crochet
Also check out the Polymer Clay Completed Project sub-board (or do a search there) for various stitch markers clayers have made.
Various kinds of things would be similar to make though using the same techniques as stitch markers, like "fan or zipper pulls," dangle earrings, wineglass charms, etc, so places online that deal with the wire or assembly techniques for making those kinds of things would be very similar to making stitch markers--except that the stitch markers would have to have a large-enough, closed
loop at the top end.
If you're interested, you can also find instructions for some of those things on these pages at my site:http://www.glassattic.com/polymer/beads.htm
(click on Misc. Uses for Beads
** for info on making loops, wrapped loops, etc, with wire, check out this page at my site:http://glassattic.com/polymer/wire.htm
(look especially at the subcategories under Basic Wire Shapes
(look esp. at Earrings
, the earwire-dangle type)
P.S. Not sure what you mean by "clasps
for crochet," or if you want to make more than one kind of thing...