You are wrong, limit of querystring is not 255 characters.
You can set the querystring limit in web.config
<system.web>
<httpruntime>
maxQueryStringLength="99999" />
</httpruntime></system.web>
Apart from passing querystring, you can use Cross Page Posting.
Here is a link, which will give you a fair idea to start
http://msdn.microsoft.com/en-us/library/ms178139(v=vs.100).aspx[
^]
cheers