Official letters usually begins with
Уважаемый (name and patronymic here)!
(in case you address to a woman it's уважаемая, of coures)
And it ends with
С уважением, (your position and name here)
And keep in mind several issues:
- If you mention dates be sure to use DD/MM/YY format instead of MM/DD/YY. (That is really confusing when October, 7th turns out to be 10 Июля, а 8 Марта оказывается August, 3rd).
- Use Вы instead of вы when addressing to someone specific.
- Make an indent at the beginning of each paragraph.
- Official title of a person you are adressing to is mentioned in a separate block in the top right corner.
Code:
Президенту Российской Федерации
В.В. Путину
(An optional part)
от Пупкина В.В.
(additional info like the address)
Уважаемый Владимир Владимирович!
Бла бла бла бла блаблаблаблаблаблаблаблаблаблаблаблаблаблаблаблабла
блаблабла ....
С уважением,
(If you've mentioned your name earlier just sign here)
Директор Советского Союза,
Василий Пупкин
Much creativity here wouldn't probably worth the effort.
As regards informal greetings you could turn loose your imagination - anything will go (and avoiding the common clich