Freely available TR4 files were used by fans to make a ton of new episodes ranging from single levels to whole new locales.
http://www.trle.net/

I'll link to my old thread
http://www.gog.com/en/forum/general/so_much_free_tomb_raider_it_hurts

Sticky-ble stuff? Looking cool, I'll probably pick up the series and maybe play some of the mods soon.

The best part is that most of the mods come with own exe hacked for some new features (hacking approved by Eidos), use assets from the openly available editor (or even custom graphics and sounds) and don't require the original games in any form.
Search that archive for The Apartment. That's Lara Croft meets Silent Hill 4.

And since TR4 got released, I'll just remind about the reminder, because most mods were built for that engine level.