You can use the code below to retrieve all acounts.
QueryExpression query = new QueryExpression();
query.EntityName = "account";
query.ColumnSet = new AllColumns();
RetrieveMultipleRequest request = new RetrieveMultipleRequest();
request.Query = query;
RetrieveMultipleResponse response = (RetrieveMultipleResponse)CrmServiceUtility.CrmSdkService.Execute(request);
Besides the above I would also recommend that you use the PageInfo property of the QueryExpression class. This will ensure that your application does not time out when displaying large number of accounts in a custom web application.
Hassan.
Hassan Hussain | http://hassanhussain.wordpress.com/