If you picked the 2010 field of 128 using just RPI and winning (not .500 record) as the criteria, 123 teams would automatically have been in...by conference (listed in conference RPI order)
Big 12--8
Big East--13
ACC--9
$EC--7
Big Ten--7
MWC--5
A10--8
Pac 10--5
MVC--7
WAC--4
CUSA--7
Colonial--4
WCC--3
Horizon--3
MAAC--3
MAC--4
Southern--4
Big Sky--3
Big West--3
OVC--2
Sun Belt--2
Ivy--2
Summit--2
America East--1
A-Sun--1
Southland--1
Big South--champion only
Patriot--champion only
Northeast--champion only
MEAC--1
SWAC--champion only
Great West--0
The next 5 teams in RPI below 128 that would be eligible would add 1 team from these conferences--
Horizon--#4
Sun Belt--#3
Ivy--#3
MAAC--#4
A-Sun--#2