Trivia: In the part of the movie that begins with Valentine's Day, there's a shot of a store with a heart (and other Valentine's decorations) in the window. Pasted on the heart is a black silhouette of a man and woman looking into each other's eyes. If you look closely, you'll notice the silhouette is of Tom Hanks and Meg Ryan.
Trivia: Dyan Cannon, who is mentioned in the film and was married to Cary Grant (who is also mentioned), grew up in Seattle - West Seattle, specifically. The large house where many interior shots were filmed is in the West Seattle neighborhood on Sunset Drive. This house is less than two blocks down from where Dyan Cannon's father was living on Sunset Drive at that time.
Answer: Ray Charles is the singer who performs this version of "Somewhere over the Rainbow" - this is not on the original movie soundtrack, but you may be able to find a Ray Charles album where this song is included.
I found an album by Ray Charles "Genius Loves Company By Ray Charles, Ray Charles And the Count Basie Orchestra" where "Over the Rainbow" is one of the songs, but it's not the same rendition as in the movie "Sleepless in Seattle." I can't fine the movie version anywhere.
Try the Ray Charles album "Genius Loves Company." It's a collections of duets and he sings "Over the Rainbow" with Johnny Mathis. It was supposedly recorded sometime between 2003 and 2004, but his lines sounds like what's in the film. So I don't know if it's just him reprising an older version he did that was used in the film, or if it's the older version with Mathis' lines mixed in. I couldn't find anything earlier.
Bishop73