I live in Dallas, TX and I was wondering what kind of flowers will attract bee's to my vegetable garden?
Just about any kind of flowers will attract bees. I have salvias, roses, citrus in bloom, lantana, nemesia, catmint, asclepias, just about anything will attract bees. Of course, if you have vegetables in bloom that need pollinating, that will attract them, too. Tomatoes and peppers and a lot of other things are pretty much self-pollinating, though.
The bumbles love the tomatoes around my yard.
They love lavender and rosemary, they may not be cold hardy enough for you though....
If you have the space, everbearing raspberries are a big draw for bees, mainly bumblebees. Our raspberry patch starts to bloom in July, and continues to flower well into October. There are always bees in there when the weather is nice. Also, it helps if no weed 'n feed is used on the lawn, in other words, no herbicide on the lawn.
There are actually blends of wildflowers made specifically for pollinators. Most of them contain several clovers. An excellent source for wildflowers and grasses is Stock Seed Co. out of Nebraska.