Understanding Colour Modes

CMYK: for use in any process colour print job. In most cases, unless it's an extremely large print run, your printer will be doing a process (CMYK) job and will require this version of the file. Colours are slightly less saturated than their RGB counterparts, but have been adjusted to maintain as much consistency as possible. Use this file in your home printer and to send to a print shop. (Tip: before running a full job at the print shop, ask for a proof. Different printers, like different monitors, output colours differenly. You want to be sure the colours are to your liking before you print 10,000 business cards.)

RGB: for use in websites, emails, presentations, and anywhere else the logo is to be viewed primarily on-screen. You can print an RGB file, but you'll find there will be a greater disparity between what you see on-screen and what your printer spits out. Keep in mind that different monitors display colours differently -- these files have been prepared on a colour-calibrated machine in order to maximize consistency across different machines, but there's no way to guarantee how someone else will see a colour.

Pantone: for use in large print jobs using Pantone inks. Pantone inks are specific colours produced by Pantone and purchased by a print shop. Unless process (CMYK) jobs which mix four different colours of ink in order to reproduce any range of colours, Pantone jobs are run with very specific ink colours. This means that there is an additional charge for every extra colour used in the print job (black is considered a colour), but you can guarantee that every time your logo is printed, it will appear with the exact same colour scheme (barring some variation caused by the print stock). Pantone colours are still used by large corporations but are falling out of favour for small print runs due to their increased cost.