Assuming you have a European Pear, two pollination charts I found on the Internet:
http://www.raintreenursery.com.....opear.html
http://www.hartmannursery.com/.....nation.htm

For best result pick one that overlaps with your tree's bloom time. It will be difficult to know what cultivar (cultivated variety) of pear tree you have if it has never produced fruit. In that case you might want to pick two different pollinators to graft into your tree.

If your yard space is limited (you don't want to plant additional trees) and your trees have several large scaffold limbs, you might consider cutting off a limb about 1 1/2 to 2 feet from the tree's center and top grafting a new cultivar into each cut limb with cleft grafts. This will make a Fruit Cocktail tree producing different varieties. Select early and late maturing varieties so you can extend your harvest. You can also select a variety that stores well so you can put some into your refrigerator to keep through December. Also, try to select those with resistance to diseases typical to your area. Don't fall into the same trap that most home orchard growers do by planting the varieties that you are familiar seeing at the grocery store, these are often not grown locally and require different climates (growing seasons), special ripening procedures, and lots of pest and disease management.

Pear grafts seem to be fairly easy to obtain success, (I have had good luck anyway, compared to my efforts on peaches and cherries). Bulletin 818 from the University of Georgia has good instructions and photos on how to perform Bud, Cleft, Whip, Bark, and Notch grafts.
http://pubs.caes.uga.edu/caesp.....d/B818.htm

Best results are obtained when you use dormant scion wood obtained in mid-winter and grafted to your trees just as they come out of dormancy in the spring. I think cleft grafts have a better than average suscess because the cut limb is dead-headed and the grafts get a lot of nutrition. I use rubber electrical tape to wrap the grafts (not the cheap vinyl stuff). Rubber tape will deteriorate during the summer preventing girdling of the graft whereas the vinyl tape needs to be cut after a couple months. Use short pieces of scion wood to reduce the transpiration losses. Seal the cut ends and any open/unwrapped joints with grafting compound (asphalt).