Do you agree with me that creating a responsive website design is an easy task? No? Hm...scroll down and I'll show you the most simple way to do it.
My advice is concise: use CSS frameworks! Hundreds of web developers have spent thousands of hours building, refining and supporting them. A framework is nothing more than a collection of preformatted classes and functions. So why you still don't use its advantages? CSS is a brilliant style language of the web. With its help, you can easily change fonts, colors, content boxes, alignments and many other effects! Moreover you don't need to touch HTML to do this. Cool, isn't it? So now you know the secret of my good mood :))
I've showcased for you the hugest list of responsive CSS frameworks. I feel they are worth your consideration. These 37 frameworks will help you in your development. You can easily choose the framework that is right for you. Enjoy !
Foundation
Foundation is a responsive front-end framework that was developed with Sass - the awesome Web technology that helps you build better and faster.

YAML
If you want to create cool design the YAML framework is just right for you! Features: flexible grid system, optimized typography for all standard elements, well prepared for HTML5 and CSS3, very slim framework core (4.6 kB)

Gumby Framework
Gumby Framework was built to be the most malleable grid framework you've ever used. The Grid lets you lay out pages quickly and easily in a natural, logical way.

ResponsiveAeon
This framework is based on HTML5 and CSS3. It contains a responsive grid all based in percentage with mediaqueries, html5 starting point and javascript.

Less Framework 4
This CSS grid system called Less Framework contains 4 layouts and 3 sets of typography present. Layouts: default (10 columns at 992px), mobile (3 columns at 320px), tablet (8 columns at 768 px), wide mobile ( 5 columns at 480px).

SimpleGrid
SG is a cool simple responsive framework for 4 distinct ranges of screen size: screens < 720px, screens > 720px, screens > than 985px, and screens > than 1235px. So people visiting your site will receive a layout that's tuned to the size of their browser window. Say goodbye to horizontal scrollbars.

Golden Grid System
Golden grid system is a folding grid for responsive design that can easily cover any screen sizes from 240 up to 2560 pixels

Responsive layout

Semantic Grid System

Amazium

Skeleton
A Beautiful Boilerplate for Responsive, Mobile-Friendly Development

1140 grid

320 and Up

The Goldilocks Approach

Inuit.css

BluCSS

Gridless

Columnal

FBG system

Frameless

Bootstrap

Boilerplate

Tiny Fluid Grid

The 1KB CSS Grid

Susy

Sass

Ez-css

Gravity

Compass

Less

960.gs

Formee

Kflorence

FluidGrids

Responsive

PhotoFluid

Gridpak.com

Articles to read:
If you need some information on how to use frameworks, its pros and cons you should visit these posts. There you'll find a lot of useful information. Take a look :)
Dive into Responsive Prototyping with Foundation
Developing WordPress Themes Using Responsive Frameworks
Building a Responsive Framework
Road testing responsive web design css frameworks
Hope this post was useful for you and you've found a huge piece of information. Frameworks are a very cool tool for you if you create more than one website per month. It may take some time to getting closer with it, but in the end you'll save some time.