There is a very nice website with many (royalty free) reference photos for artists, and I wanted to share this with you:
http://www.human-anatomy-for-artist.com
This gallery only offers men and couple photos, for female anatomy they have an extra gallery:
http://www.female-anatomy-for-artist.com
I gave it a try: 3 months subscription (individual membership), for US$46 -> you get unlimited downloads, access to the zip files (if you choose the 1-month-subscription, you "just" can download the single photos (no zip files) and have a daily limit of 250 downloads).
I can really recommend that site:
* 20 GB of high resolution photos (men/couples)
* Working search form (gender, race, age, pose,...)
* Photoshootings are available as sets (zip includes all photos of a shooting)
* Photos are royalty free
* Updated frequently
* You can suggest/request poses if you need something special
* Quick personal support when there are problems
You have to get a payed account to get access to the high resolution photos (except some free samples on the website).
So if you need good references for improving - check out this site. :)