Today I come up with some useful list which help you in web development and good news is that its all free.
1) “FIREBUG” :-
Basically “FIREBUG” is add in for FireFox. It’s a great utility helps a lot to design web pages. As a developer I am mostly intrested in programming not designing.But this utility help me in solving designing issues. With the help of it you can manage designing ,CSS issues.
You can download this from https://addons.mozilla.org/en-US/firefox/addon/1843
2) Web Development Helper:-
This one is another useful utitly for web developer to improve performance. Its basically help you to determine which page taking how much time to response.It also help other area also like script finding. It has dom Inspector also. You can take help of this tool in various way.
You can download this from http://projects.nikhilk.net/WebDevHelper
3) Deep Zoom composer:- If you are working on Silverlight also then you can use Deep Zoom composer.it has very nice feature for images.
You can dowload this from http://www.microsoft.com/downloads/details.aspx?familyid=457b17b7-52bf-4bda-87a3-fa8a4673f8bf&displaylang=en
So just dowload & use this tools and improve your code.