Medium Size Shadchan:
(This is something between a translation and a summary.)
The Radak:
Question: Why would Tzadikim, whose intentions of marriage are to progenate, seek beautiful women? Yaakov chose Rachel because she was beautiful, and was upset at Lavan for giving him Leah, because Leah was less beautiful. Why would he do this?
Answer 1: In order to increase their progeny, they wanted to arouse their desire, hence they would choose beautiful women.
Answer 2: They wanted their children to be beautiful and to look like them.
Answer 3: Having her form in front of him will gladden him and man is supposed to be happy in his world and with the portion that H’ gives him. H’ provides the righteous with beautiful women as he did for our forefathers and other righteous people, so that they should be happy with their lot and have kids like themselves.