Hehehe, I might get to a BG playthrough once I finish with the Elder Scrolls games, which are really long and detailed. So far, I've been having a blast with role-playing there.
As for the touch spell + an off-hand weapon, it's easy.
On a F/M, my default weapon (at the start of BG1) is a throwing dagger, with a ninja-to equipped in the off-hand (2 pips in daggers and scimitars respectively). When I cast Cold Touch, it switches to the touch spell + the off-hand weapon. Imagine the possibilities when it comes to BG2 with speed weapons in the off-hand.
This touch spell has THAC0 defined by your class and STR, same for the off-hand weapon. No penalties for dual-wielding. It also feels cool to use touch spells, finally. And
@Blackraven noted that you can even dispel the touch spell if you don't need it by shapeshifting with Relair's Mistake or the Cloak of the Sewers.