*UNFORTUNATELY THIS IS ALL OUTDATED NOW, SORRY*

BTC Trading Corp. - https://btct.co

Pros: good notifications in email, good analysis of your positions

Cons: always in development, weird UI when new features are added, 24 hour withdrawal limits, but you can request larger amounts but it is delayed a few hours as the admin has to move the bitcoins from cold storage

BitFunder - https://bitfunder.com

Pros: looks more advanced than BTC Trading Corp

Cons: stock prices are typically lower there on cross-listed securities, no email notifications when anything happens, lame we-exchange thing

Havelock Investments - https://havelockinvestments.com

Pros/Cons: Best UI UX, Canada.

MPEx - http://mpex.co

Pros/Cons: Run by a multiple personality lunatic.

Cons: Admission/Listing fees, I forget. Nonexistent UI

I've used BitFunder I've not used any others so I can't speak to the pros or cons of each. With BitFunder you have to use WeExchange to transfer your coins to them which is a bit of a pain instead of being able to just deposit directly.

I recently started using cryptostocks.com for BTC/LTC/DVC denominated 'stocks'. It has a varied selection of companies (with dividend payments and even some rudimentary option writing/trading system), it's easy to use and quite affordable (except for issuing your own shares, which requires a hefty fee). Nothing to complain about so far, but I haven't tried to withdraw funds yet.

EDIT: I've had some success with predictious.com (binary options on real world events), however the volume is frustratingly low.