Well there are not that many, and as for weight...not much either. I know of three exchanges off the top of my head not including havelock:
cryptostocks
crypto-trade
mpoe
Hehe, a little off.
There's a smattering of wanna-be exchanges (some run by out and out scammers, some run by people with good intentions but who are so inept they end up scamming anyway whether they like it or not), and there's
MPEx.
That's been the situation for quite a while, with various shufflings of that former group.
Here's some links you may find useful to the end of researching all of this.
Also check out
#bitcoin-assets on IRC.