Colour can profoundly affect your clients' perception of your business. The interaction between colour, fonts and other graphical elements can convey very strong messages. If you would like to read more about colour and it's effects, take a look at the COLOR MATTERS® web site. There you will find lots of information about the psychological and physiological effects of colour schemes. Also, you may wish to look at the Pantone® web site.
There are lots of colour scheme management tools available on the web, and many of them produce colour codes that can be used by web developers. I particularly like this one from 'pixy' that can output colours in HSB and HEX formats. It provides a mix of colours that are consistent with colour theory to produce a suite of colours that can be used for you next web and/or print project.
Fonts are still problematic on the web. It really depends on what operating system is being used to view web pages, and what fonts are available to that operating system. This really does reduce your choice here. It is usually best to use font families rather than individual fonts, which may not be available on the system that the viewer is using. Font families allow us to specify a preferred font, plus some alternatives, depending on the operating system used by the browser.
Choice of fonts for menus, other navigation and body text can profoundly alter users' perceptions of you business identity, and yet are still severely limited by the available technology (in my humble opinion!).
Here are some examples reproduced in bold:
Note that these fonts may not look identical on all browsers and operating systems.