Letters in Spanish
If I write to a friend . . . . Querida Amiga, Mi Bien, Mi Querida? (Any others ?) But how to end? Adios, Siempres? (Or their equivalents)
If I write a business letter . . . Estimado Senor, Estimados Senores, (Any others ?) But then how "Yours truly, or Sincerely ?" (Or their equivalents)
Thanks in advance. Gracias de antemado.
To start a letter to a friend you can also start with "Mi querida amiga", "Querida [her name]" or simply her name, depending on the familiarity between you two. And to end you can easily say "Chao, un beso", "espero (con cariño) tu respuesta", or you can make up something based on one of the topics of the letter. But "un abrazo", as Samsta said before it's great too.
For a business letter "estimado [whoever it is]" works perfectly. When it comes to the end, might depend on the matter of said business. To a boss or an interview and similar, those you said are great; for an "informal" business, "Un saludo/Saludos" is fine too (short and simple, I'd never use it for something really important).
I hope this is helpful. Suerte :)