you have to define DataTextField and DataValueField as well. Try using SqlDataAdpter :

DataSet lvDS = new DataSet();
SqlDataAdapter myda = new SqlDataAdapter("select [Client Name] from Accounts ", conn);
myda.Fill(lvDS);
ProvTab_Client_DropDown.DataSource = lvDS;
ProvTab_Client_DropDown.DataTextField = "ClientName";
ProvTab_Client_DropDown.DataValueField = "ClientId";
ProvTab_Client_DropDown.DataBind();

more here:

http://www.progtalk.com/viewarticle.aspx?articleid=194