I'd have to say my favorite songs are: Anytime, Born to Love You, Castles on Quicksand, Change is in Your Hand, Handle it with Care, If It Wasn't for You, Let Me Be the One, Let's Spend Some Time Together, Love is Not Like This, Must Be Love (sung by Mark), Never Give Up, Next Big Thing, She's Not You (sung by Jake), So Glad I Was There, Someone to Hold Onto, Stand Back, Stand Together, Take It Higher, Tell Her I'll Be Waiting, The Way We Are (sung by Mark and Sam), the Theme Song (Season 1 and 2 version), the Theme Song (Season 3-5 version), To the End, Too Much to Dream, What Will I Do With my Heart, What Would I Do (Without You, and Whenever I Think of You.
I've realized that I've got 38 of 40 tracks on my computer (I'm missing Matt's version of "Must Be Love" and Matt and Sam's version of "The Way We Are", both because I couldn't find studio versions of those tracks).