Output code behind variable on aspx

Hi all!
I have a aspx page with a codebehind page with lots of code in it. Sometimes i want to display a popup window. How can i output a string variable with my javascript on my aspx page? If I use response.write from the code behind my code will be on the top of the page and not were I want it to be. If I use an asp:label i get unnecessary div tags. Is there a way to make a variable public so i can use it on my aspx page or is there maybe a more suitable control for this?