I always keep a bundle or two of La Floridita Maduro on hand ...
... really inexpensive (about a dollar each), but a well balanced cigar full of flavor, plenty of 'medium-bodied' but smooth smoke, and a great burn ... so they are not turned off by the experience.
On the other hand, if you give them a really surpurb 'top-shelf' cigar that is not too overpowering, they may not put it down after a few puffs ...