This is probably my second-favourite song by Robbie Williams, following "Angels":
It's "She's the One", taken from Williams' second studio album, I've Been Expecting You, and was included on The Ego Has Landed, which is his first compilation album. The song is often thought to be an original by Williams but a band called World Party wrote and composed the song initially; however, Williams' cover is definitely the most known version.
I wrote about "Angels" here and first mentioned Williams himself in an early post of mine. Both it and "She's the One" were the first of his songs I properly heard, not including anything he sang with the band Take That or any of its members or anything I heard in a film.