TSQL or SSIS convert Columns into Rows

Could anyone please suggest how to achieve the following开发者_JAVA技巧? i.e. convert columns in to rows using either TSQL or SSIS:

e.g. from this:

col1    col2
start   end

to this:

start
end

from this:

col1    col2    col3    col4
start   break   start   end

to this:

start
break
start
break

Thank you.

Thanks @Dalex for your answer.

Since I'm using SSIS I ended up using Unpivot Transformation Task which required no code.