In general, the prefix and suffix list follows standard b.net in terms of what can get what. So these 2 links:
http://classic.battle.net/diablo2exp/it ... /pre.shtmlhttp://classic.battle.net/diablo2exp/it ... /suf.shtmlShould cover most of the "what can spawn on what" questions.
Circlets are indeed a special class. Again, standard b.net rules apply here for circlet class items:
http://classic.battle.net/diablo2exp/it ... lets.shtml Also note how many times "circlets" appears in the first 2 links and you will see that circlet class items are special.
I assume you have also seen our crafting page on
http://blue.arimyth.com/