https://www.betonmarkets.comAlready takes Liberty Reserve, Ukash and a number of other payment options as you can see here:
https://toucan1.betonmarkets.com/d/available_payment_methods.cgi?l=GBIt should not be too difficult to get them to accept Bitcoin, especially considering their international client base. (They even list e-gold as a payment option!, clearly outdated).
http://www.intrade.comActually had to leave the US and domicile in Ireland because of US gambling restrictions... Bitcoin would be a perfect fit for them too.
There is even a betsofbitcoin bet (not mine) on when they will accept Bitcoin:
http://betsofbitco.in/item?id=953In general speculation, trading and betting sites are all good bitcoin fits.
Any other similar sites that you can think of?