The Sims 3

16:10, 15:9 and 16:9 are natively supported with Vert- gameplay, the FOV Hack makes it Hor+.

By default The Sims 3 is Vert-, which does not hurt the gameplay in widescreen really.
However, Racer_S designed a FOV Hack for TripleHead that also works for widescreen. Check the Racer_S Hacks & Mods page for the download (check Links for URL).

Extract ts3FOV.exe to any folder and run it. Check Auto Enable and move the FOV slider to one of the following values, assuming 860 is the game's stock FOV for 4:3 (I think it should be 825, but that's negligible) :

1030 for 16:10
1075 for 15:9 (1280x768)
1140 for 16:9

Run the game, enjoy. Be sure to use the mouse wheel to zoom in and out while the Hack is active, not the Numpad + and - keys !

Due to the way the camera works in Create-A-Sim mode, a single FOV value is not enough to achieve real Hor+. The far view's a bit Vert- while close-ups are Hor+/Vert+. So feel free to disable the FOV Hack in CAS mode. Either way, everything is always functional and visible in widescreen.