in the course of my browsing i find all kinds of unreliable (no names or incorrect names) images. might be great to look at, but not exactly a reference.
so today i found this flickr collection from german gottingen bot-garden. since bot gardens usually have labels, at least then you can be assured of accuracy of names.
https://www.flickr.com/photos/...
i'll try to add some other sites as i find them. i've seen some in latam bot-gardens too.
hope, other people can post their findings here too
it would be great to have a ready pic-ref and also nice just to flip thru it in free time!

Nice photog on that site.

Very reliable.
http://abrimaal.pro-e.pl/arace...

Marek Argent, who owns/maintains this site, has moderated the I.A.S. plant ID forums for many years. The names and photographs on his site reflect this.

oh, this is a very well organized site! and very nice to see pics side by side - very convenient! thanks!
here's hawaiian bot garden site on big island, north of hilo.
http://www.htbg.com/search.php...

Love the photography skylark. I think you'll have fun with these too.

Here are a few other very reliable sites:
http://www.aroidpictures.fr/GE...
http://www4.ncsu.edu/~alan/pla...