this is actually how i found this site!! i put a general search on google about which car fit 3 car seats in the back, and someone else had asked the same question here!!
i ended up with a BMW X5 (my oh worked for them - it's not what you know but who you know!!), and i must confess, i know all about the yuppie bits etc, but i would recommend a 4x4 to anyone with more than 1 kiddie, as there is no hassel with prams and shopping in the boot at the same time etc. i can fit all the seats in - just!! and it means after we didnt go anywhere as a family for 9 months, we now do!!