I think this is one of the most difficult Pre-flop questions.
On the one side, you sometimes are getting as much as 10 or 12-1 to play; on the other side, hands like T7o (2-gap offsuit connectors) make good hands so rarely. Even worse, hands like these put new players in very tricky spots (e.g. how much money are you going to lose when you don't know how to fold 2 pair on a T[img]/images/graemlins/spade.gif[/img]9[img]/images/graemlins/heart.gif[/img]7[img]/images/graemlins/spade.gif[/img] board to heavy action.
Completing with crap from the small blind was one of my biggest leaks for my first 4 or 5 months. I have two very solid friends who first got me into hold-em awhile ago. I asked them this question early on when we were taking a break at from B&M play. Their advice was "with 4 or more limpers, complete with any two cards." After awhile, I began to think more independently and I realized that this was terrible advice.
OP, READ THE FOLLOWING ANALYSIS AND THEN REFINE YOUR QUESTION.
http://www.pokerstove.com/analysis/unsuited.php