A letterhead is an important part of a business's overall packaging.  Like brochures, print advertisements, posters etc. the letterhead is a constant representative of the business.  It is a business card that is handed out on a daily basis. It helps build brand recall and reinforces brand identity.

Colour
In terms of cost there is very little difference between four colour and single colour printing costs.  It really all depends on how much colour really features in your logo. Some letterheads look better as a single colour, whilst others rely on colours to better communicate the brand.

Selecting papers and weight
Selecting paper weight and texture can also be important in the image you are trying to portray of your company.  If you opt for a cheaper paper that doesn't have much weight to it, you run the risk of coming across as cheap and unprofessional.

Reinforce your brand identity
A letterhead should reinforce your brand identity.  You could argue that a letterhead is not like a brochure or poster, but it will be sent out to hundreds of people if not thousands and its marketing potential should not be underestimated.

Envelopes to match
Once you have your letterhead design, consider printing envelopes to match that again reinforce your company's brand identity.

Email
We probably send more emails today than letters, so make sure the look of your letterhead is consistent with the look of your email newsletter headers and email signatures.