To avoid having a thread about recommendable aircraft add-ons every odd couple of days, here are two lists compiled by the folks at Sim-Outhouse.
FSX native freeware aircraft:https://docs.google.com/spreadsheet/ccc?key=0Ajp_sOJLki7mdEJiNWhQbmU2czVZUzU4YWgzYm1oVXc
FSX native payware aircraft:https://skydrive.live.com/view.aspx/.Public/Native%20FSX%20Payware.xls?cid=408ca931940d5e3c
"Native" = Built to FSX's model format standard and thus supporting features like spec and bump mapping
Are these lists complete?
Certainly not, but you've got quite a bit of stuff to waste your money and/or time on for a start.
Mods: I suggest pinning this thread to the top of the forum.