Looks like Crabgrass. Look for a product that can get rid of it.

Crab grass or goosegrass are my first two guesses. You can kill crabgrass with specialized weed killers. goosegrass is a different animal(plant). It is immune to almost all of the residential available herbicides.
If its crabgrass, take a look at quinclorac (sp) generics, it works well.
Im sure others will chime in and pinpoint what it is.

The problem with weed n feed and weed b gone is that they target broadleaf weeds. This is a grass type weed.

You should not have to use an herbicide if you are taking good care and have a dense turf. If your turf is thin, then you likely have fescue and will need to reseed/overseed every fall. If you have Kentucky bluegrass and are getting weeds, then you are not taking proper care of it. Here are the basics of lawn care.

1. Water deeply and infrequently. Deeply means one inch all at one time. Measure how long it takes to apply one inch by setting out some cat food or tuna cans. Then always apply for that length of time. Infrequently means once per week if the temps are in the 90s, once every 2 weeks if the temps are in the 80s, and once every 3 weeks if the temps are in the 70s.

2. Mow at or near your mower's highest setting. This works for most grasses except dwarf varieties and bermuda, centipede, and creeping bentgrass.

3. Fertilize 3x per year if you are using chemical fertilizers. Apply once in late spring (Memorial Day), once on Labor Day, and once around Thanksgiving. Be sure to wash the fertilizer down to the soil immediately after applying. Morning dew the following day can kill the grass if you do not get it dissolved the same day you apply. If you are using organic fertilizer you can apply any time you want. Organics do not need to be washed in.