The History Of Lucy Sponsorship
Philip Morris was "I Love Lucy's" sponsor from the very first episode on October 15th, 1951. (A series of announcers did the PM cigarette spots, as did Lucy and Desi themselves.) By late 1954, it was clear Philip Morris was losing ground in the cigarette race to the up and coming filters, and fast-growing Pall Mall from American Tobacco, and the company decided to phase out its sponsorship of the series.
In January 1955, Proctor & Gamble became "Lucy's" alternate sponsor, pitching Cheer and Lilt home permanents every other week. Philip Morris became a co-sponsor for the remainder of the 1954-55 season, until its contract expired.
Starting with the 1955-56 season, General Foods joined P&G as alternating sponsors (Lucy and Desi would do commercials at the end of the show for the remainder of the half-hour series' run.) The only exception was for a few weeks in early 1957, when Ford Motor Company purchased time on "Lucy" to promote the Ford division lineup, including its new Skyliner retractable hardtop (with a commercial featuring Lucy & Desi).
For the fall of 1957, when the "I Love Lucy" format switched to occasional hour-long programs, Ford agreed to sponsor five "Lucy" specials during the 1957-58 season. Westinghouse, of course, became the "Desilu Playhouse" sponsor from 1958 to 1960.
When CBS began airing "Lucy" reruns on weekends in 1955, Lehn & Fink (Lysol, Hines hand cream, Dorothy Gray cosmetics and other products) sponsored those shows. CBS also aired "Lucy" reruns in prime time from 1957 to 1959; General Foods and Clairol were the sponsors there. And in 1960, CBS aired the final "Lucy" half-hour shows as "Lucy In Connecticut," sponsored by General Mills (Cheerios and Gold Medal Flour).
To the best of my research and viewing (including my own vintage TV collection), that pretty much sums up the "I Love Lucy" sponsorship history.