Natural landmarks are pretty well represented thanks to X-Plane's detailed terrain mesh. Mt. St. Helens, the Grand Canyon, etc. are all instantly recognizable and the detail can even be improved with optional higher-resolution mesh downloads.
However, one of XP10's current shortcomings, especially if compared to default FSX, is the lack of man-made landmarks. It's possible that, with the recent introduction of the new version of World Editor, we may see the state of XP10's default landmarks gradually improve, but for the time being you do have alternatives.
First: payware. There actually isn't a lot of payware dedicated to introducing landmarks into the world--most efforts have been focused on airports so far. Some packages, like
this San Fransisco add-on or the recent
Glitter Gulch, aim to cover a wider area and include as many landmarks as possible. (The latter is, in fact, going to be periodically expanded (for free) with additional hotels and casinos as they become available.)
Second: freeware. I dunno about you, but free is my favourite number. XP has a bustling, dedicated freeware scene that has produced some fantastic content, some of which outstrips the quality of many payware add-ons for any sim. Depending on where you like to fly, coverage will vary. France is particularly well represented thanks to the efforts of the folks over at
XPFR. If the Eiffel Tower is what you want, be sure to take a look at the
Ville de Paris download. Canada also has a number of good landmark packages available, including
Montreal and
Toronto, which is one of my favourites:
Not every area or city is as well represented, but hunt around the various XP hubs and see what they have to offer.
Third: conversion. If you have some FSX scenery lying around on your hard drives, you can try converting it for use in X-Plane with a handy little freeware tool called
FS2XP. I've been experimenting with this method recently using freeware FSX scenery and it's been a bit of a mixed bag. If objects depend on default FSX textures, they're import as blank, white monoliths; however, if the objects are 100% custom made, they'll make the transition just fine (
Quebec City turned out pretty nicely, as did
Cardiff). Payware FSX sceneries seem to work well; over in the screenshots forum, Scoobe recently posted some pics of Aerosoft's Manhattan converted for use in X-Plane and it looks amazing. EDIT:
Here's the thread. The shots of NYC are converted, and those of Las Vegas are from the Glitter Gulch payware I mentioned earlier. Here's
another thread that demonstrates a converted Chicago payware.
Hope this helps. Let me know if you have any questions.