Ditto on a lot of previously mentioned items.  But don't forget SweetFX.  It really added to my sim.

NL2000, is a complete freeware scenery of ALL of the Netherlands.  Includes airports too.

Very nice scenery indeed, considering it's free. And do not forget the freeware FSX scenery from Max Kraus, Mauritius FIMP, Gantly Adams TBPB, Gold Coat YBCG and Paphos LCPH. All available at Avsim's library.

Ant's Tiger Moth is the only freeware airplane on my hard drive.  Hardly a tubeliner,  though.