realize that budget plays a huge factor. builds can range from as little as a few hundred dollars for a low end budget system to over ten thousand dollars for a top of the line system. keep in mind that once you top a certain price point, your value for the dollar starts to decline. the average person does not need a $10000 system. normally prices for top of the line systems range between $2000-4000 depending on your particular wants and needs of course.
as far as my opinion on what i would personally build if i was given an open budget? it would require more research but off the top of my head this is what i came up with.
corsair obsidian case or other high end full sized tower
intel i7 3960x extreme unlocked socket 2011 cpu
asus rampage IV extreme socket 2011 mobo
mushkin ram to fit mobo specs, minimum 12gb
4x evga gtx 690 gpu
4x ocz octane 1tb ssd in raid 1+0/0+1 or similar
4x ocz octane 1tb ssd data drives
1200-1500w psu evga, pcp&c or asus. depending on power demands.
full dangerden watercooling system for all gpu, all ssd and cpu. full thickness extreme radiators with delta fans. delta fans and fan control for ambient airflow.
3x 1920x1080p 8bit ips lcd panels 22" to 24"
1x 40" to 50" 1080p television
das, deck or similar mechanical keyboard
logitech g9, razer deathadder or similar mouse
pioneer home theater receiver
klipsch quintet 5.0 speaker set and 450w subwoofer. or if you want to go crazy a full set of tower speakers.
realize that we are talking about a system and perepherals totalling $30000-40000.
can we go that insane? sure we can. is it practical? not really.
more practical is $2000 for the tower, $1000 for perepherals.