The link that FireTigris posted is the very best Sexlink page on the web!!!
White Leghorns very rarely have the proper genes for making sexlinks. RIR roo x White Leghorn hen will make all white chicks the vast majority of the time.
White Rocks are also not a very good choice. (copied from Tadkerson's sticky) "White Wyandottes and White Plymouth Rocks are not a good choice. They sometimes have the correct genotype to produce sex linked chicks and at other times, they do not have the correct genotype to produce sex linked chicks."
Great choices for the female of a red sexlink cross include (easy to find breeds I made bold): Rhode Island White, Salmon Faverolle, Light Sussex, Columbian Leghorn, Delaware, Light Brahma, Dark Brahma, Columbian Rock, Columbian Wyandotte, Silver Penciled Rock, Silver Penciled Wyandotte, Silver Laced Wyandotte, Silver Leghorn, and Silver Welsummer.