Stockholm
 

I'm planning a week in Stockholm and Oslo, are there any city nearby I should consider? any ideas of a site or recommendation of guide to follow for a few days?

Probably Munich and Bodrum :-)

msalinasg: Do you mean a week in each city or a week between the two? Please note that the two cities are far apart and you will spend the better part of day getting from one to the other unless you fly. An overnight train is an option.
We will know more about how to help you when you explain your time.

I concur with the other posts. If you want a good day plus trip I strongly suggest you go to Tallinn in Estonia. It is a village which dates back four centuries and is perfectly restored.
It's worth it.

On the other hand, a trip to Helsinki,
Finald is a lot closer than Oslo. It too is a charming for a day visit.

However, there is a lot of things to do and some excellent museums, plus the old city which could easily fill the week.

There are many sites to see in Stockholm, among them not to be missed are the City Hall, the Vasa and the Old Town (Gamla Stan). It is very easy to hop on a ferry and head to Tallinn or Helsinki. The weather at this time of the year can be quite changeable so be sure you have layers and a raincoat.