Terrahash does not seem to be accepting preorders/orders yet, but you can get on their mailing list at their website.  KNCminer is accepting orders/preorders and apparently they've unwittingly set up some spurious off-exchange trading for the unregulated speculative derivatives "KNC preorder numbers" now recklessly being traded on bitcointalk.  That's a real joker (tearjerker?) for newbies because KNC preorder numbers are free for the taking on the real McCoy site (kncminer.com), all of which are promises (assign your level of credibility here) for September delivery.

It's a wild wild West out there.  You might want to google these terms:

Avalon
Terrahash
AsicMiner
Butterfly
BTCGarden.com
KNCMiner
Steamboat

Thoroughly research this stuff and you'll probably be in a much better position to place your bets on the upcoming ASIC revolution.  The wildcard, of course, is the exponentially growing difficulty factor for BTC.  Another monkey wrench is whether the new hardware effectively sorts through scrypt, SHA-256 or something else.