Users at BestCommentaries.com recommend Gordon J. Wenham's "The Book of Leviticus" and John E. Hartley's "Leviticus" as technical commentaries on Leviticus. Both books have received positive customer reviews on Amazon.com. Free online commentaries are available at BibleGateway.com and BibleStudyTools.com.
Amazon's summary explains that in "The Book of Leviticus," Wenham reconstructs the text's original meaning by comparing Biblical customs with neighboring cultures' practices at the time. He also discusses how the passages relate to modern Christianity to show how Leviticus still has theological value.
Hartley has similar aims in "Leviticus;" he shows how its message of worship is just as important in modern times as when Leviticus was written. He agrees that Yahweh spoke to Moses and that Leviticus influenced spiritual life in Israel.
BibleGateway.com's commentary is divided according to Leviticus' chapters, with brief articles that explain each chapter's sections. It begins with Leviticus 1:3-9, which deals with sacrifices. God gives Moses directions for sacrifices, which are to include burnt offerings.
BibleStudyTools.com also offers a chapter-by-chapter commentary that goes into detail regarding each verse and includes links to references in the Bible's other books. The commentary on Leviticus 1:3-9 explains in depth that the sacrificial animal must be a male and be the best in the herd. It includes mention of various scholars' readings.