Most grass seed used in residential lawns consists of a fairly common mix of grasses. Someone at your local garden center will be able to assist you in finding a high quality grass seed. One of the things to look for in a grass seed is the amount of inert matter. Typically grass seed has some percentage of inert matter (inert matter = empty seeds or sometimes weeds). Seed companies are required to include the percentages on the bag or box of seed. The more expensive seeds will have a very low percentage of inert matter.
When fixing patches of grass or over-seeding remember, you get what you pay for. A cheap mix of grass seed will give you cheap results. If you desire a healthy thick lawn then make sure you buy a quality seed that is low in inert matter.