I asked this question recently for Intel Desktop Boards, and the answer I got back was:
VT-d is enabled on the following chipsets:
Intel Q35 GMCH with ICH9 DO (Bearlake chipset)
The following chipsets have VT-d capability, but OEMs may not have enabled in systems based on these:
Intel X38
Intel X48
VT-d will be enabled on these future products:
Intel Q45 (Eaglelake)
For Intel Desktop Boards, these have VT-d support enabled:
Intel DQ35JO
Intel DQ35MP
Intel DX38BT
Intel DX48BT2
These future Intel Desktop Boards will have VT-d support:
Intel DQ45CB
Intel DQ45EK