1. Genie in a Bottle
This is my favourite Christina song of all. It's her debut single and was released in America in June 1999 but I think it came out around October in the UK. Genie in a Bottle is from Christina's debut self titled album and is one of her best selling singles to date, reaching No 1 in the US, UK, Ausrralia and Canada and No 2 in other countries. There's a Spanish version which appears on her album Mi Reflejo (My Reflection), Genio Atrapado (which translates as something like "Trapped Genie").
I included it in my recent Top 10 Summer Songs post.