Sql 2008 data type for 2million+ characters

Depending on the encoding type (unicode/non-unicode) you can use nvarchar(max) or varchar(max).

nvarchar(max)

As mentioned earlier nvarchar is for unicode and varchar is for non-unicode. If you don't expect unicode (e.g. foreign alphabets etc.) then varchar makes better sense as it uses one byte for storing each character, i.e. half the requirement of nvarchar, which makes a huge difference not only in storage requirements, but also in I/O and therefore in performance, especially when dealing with such large character strings.

I agree, varchar(max) or nvarchar(max), having a capacity near to 2GB

i am using this data type only , but when i use this , it truncates the data and shows , half results

Where exactly do you have this issue?

In ssms you have indeed a cutoff, but the data is there

How do you know if it's truncated the results? Please note that Management Studio truncates large data for display purposes, but the actual data in the table is probably OK. You should be able to test it using something like:
SELECT LEN(my_col), my_col FROM my_table;

Hi Angel, : )
I didn't see you've already replied... I'm using my mobile and the connection is not so fast.  

Best Regards.

hi

actually i am using one procedure , where the parameter is of type varchar(max), and i am passing a large string to it from C# application ,  and now i want this passed string to be displayed in a mail ,which is triggered from database.

is this is a problem of database mail , which doesn't accept a long string.