Frontline Plus stopped working for us a few years ago BUT I'm going to try it again this year just for the heck of it. It's cheaper than k9 Advantix, which is the only thing that worked for us the last few years.
Try to avoid Hartz products, and my step-mom found this thing at Sam's Club yesterday that she almost bought until I read tons of horrifying reviews. So yeah the main ones that are trustworthy as far as effective and safe are the Frontline and Advantix.