Offer letter, counter offer?

Since wanting a counter-offer from your current employer makes it sound as if you really do like your current job, definitely include that in your letter. As to the actual letter, I'd do something like this:

To (manager's name) of (company you are currently employed with),

This letter is to inform you that I have received another position with a different company for my abilities. I will not disclose the terms of my new employment opportunity, but needless to say, the new prospective employer is offering more money (benefits, hours, etc).However, I do enjoy contributing to this company and enjoy being part of the team. If the feeling is mutual and I am a valued member of the staff here, I am more than willing to look over a counteroffer from here. If no offer can be made or the offer made is rejected, I will be resigning my position on (date you intend to leave).

I have enjoyed my time here. Thank you,

Your name

I had a similar situation at work just a few weeks ago.

This particular employee had the gall to write her letter at work on company time and had the nerve to ask another employee to read it over...lol.

I do not respond favorably to employees who try to extort a raise by threatening to quit. If an employee is actively seeking other employment I don't want them around. By that time their efficiency and productivity has usually decreased and often they are adding negative drama to the work place.

So I wished her well, collected her key and said buh-bye. It turns out the other job didn't work out very well as she has recently filed for unemployment.

My best advice is keep the other offer to yourself. If you want to ask for a raise, make an appointment to speak to your supervisor and make your case based on your own merits. If you get a raise, great. If not, you can quit if you want to.