Don't know how to create buttons in Photoshop or just plain lazy? Generate buttons with a few clicks :>

As Button Generator

This is pretty cool. If you don't know what the golden ratio is, check out this Wikipedia article.

Golden Ratio Calculator from Design by Ninjas

Nothing can be more useful than handy tools you can use “on the fly” in your design process. Whether you’d like to generate css layouts, create vector images, format or optimize CSS code, generate patterns- you can use dozens of tools to make your life easier.

I personally don't use these kind of tools, but some may find them quite handy~

Handy Designer’s Tools “On The Fly” from Noupe

This is pretty cool :]

PodiPodi is an experimental project in Interaction Design born with the aim to give web designers a way to enhance their websites with two new levels of interaction.

PodiPodi

Response times, availability, and stability are vital factors to bear in mind when creating and maintaining a web application. If you’re concerned about your web pages’ speed or want to make sure you’re in tip-top shape before starting or launching a project, here’s a few useful, free tools to help you create and sustain high-performance web applications.

15 Tools to Help You Develop Faster Web Pages from Six Revisions

Personally I'm not a big fan of the image reflection effect, but if you're a fan then you'll love Picreflect. Picreflect has to be the 'dirtiest' way to create image reflections :p

Picreflect.com

There are many available tools to help make web development projects quicker and more productive. Aside from a handy text editor or WYSIWYG editor like Dreamweaver, you can find plenty of tools and utilities that can greatly increase development speed, reduce debugging and testing time, and improve quality of the output. The tools described below are a variety of utilities, optimizers, testing, and debugging tools aimed towards helping developers create websites more efficiently.

20 Useful Tools to Make Web Development More Efficient from Six Revisions

Sick of adding class names to table cells? Kotatsu to the rescue!

I personally use TextMate (Mac only) for its "HTML bundles", "multipurpose-ness" and its sexiness; it's totally worth the cash money.

In the list below we present an overview of 35 established or rather unknown — but useful source code-editors; you’ll probably find “usual suspects” — your favourite editor or the editor you’ve once been working with. But you’ll also find some rather unknown alternatives which are definitely worth considering when choosing an optimal source code editor.

35 Useful Source Code Editors Reviewed from Smashing Magazine

Seasoned graphic designers wouldn't dream of sending a print project to press without first approving an accurate proof. Your client's email marketing campaign should be no different. You need to be sure you know what your design looks like on the different email clients your readers might be using.

Proof Your Email Designs in Different Email Clients from Creative Techs

Every web designer has a need to create invoices and track payments that have been received or have not yet been paid. Fortunately, there are a number of tools that can streamline this process, and we’ll look at 20 options here. There is a good deal of variety in terms of features and pricing. Some are better suited for organizations that have several employees, while others may be a good fit for a freelancer. Some of these tools will simply help you to create attractive invoices and other will extend further into the area of accounting software.

20 Invoicing Tools for Web Designers from Six Revisions