Index on multiple columns

Need your advise to create indexes in the following scenario.

For example, we have a table OrderDetail with the following structure

CREATE TABLE [dbo].[OrderDetail](
    [SalesOrderID] [int] NOT NULL,
    [SalesOrderDetailID] [int] IDENTITY(1,1) NOT NULL,
    [CarrierTrackingNumber] [nvarchar](25) NULL,
    [OrderQty] [smallint] NOT NULL,
    [ProductID] [int] NOT NULL,
    [SpecialOfferID] [int] NOT NULL,
    [UnitPrice] [money] NOT NULL,
    [UnitPriceDiscount] [money] NOT NULL,
    [LineTotal] [numeric](38, 6) NOT NULL,
    [rowguid] [uniqueidentifier] NOT NULL,
    [ModifiedDate] [datetime] NOT NULL
) ON [PRIMARY]

We use this table in several select statements with various clauses.

1) select salesorderid,CarrierTrackingNumber,orderqty, unitprice,modifieddate from OrderDetail
where productid=776

2) select salesorderid,productid, CarrierTrackingNumber,orderqty, unitprice,modifieddate from OrderDetail
where productid in (775,776,800) and orderqty>2

3) select salesorderid,productid, CarrierTrackingNumber,orderqty, unitprice,modifieddate from OrderDetail
where modifieddate between '01-01-2010' and '01-01-2011'

4) select orderqty, unitprice,modifieddate from OrderDetail
where productid=776 and orderqty<4 and modifieddate between '01-01-2010' and '01-01-2011'

have tried creating indexes with combinations, but ended up with scans and lookups.

Thanks,

Shiva