Tenba Shootout (large) fits that bill perfectly. Bought mine about 4? months ago at a local B&M shop for $175.
It will comfortably* hold:
K10D & grip w/ 18-250 attached
K20D & grip w/ Tam 16-50 attached
Tam 90mm macro
Tam 75-300
FA 50/1.4
M 50/2
Vivitar 285HV flash
Cokin filter case
24 AA batteries & 4 spare batts for cameras
Panasonic GS320 MiniDV camcorder
Rocket blower & cleaning gear
Toshiba 15" widescreen laptop
Bogen/Manfrotto 055XBPRO tripod
... and still have room in a side pocket for a sandwich without smashing it.
* comfortably is relative to the strength of your back. YMMV