Here is a short list to get you started, I had put it together for a friend who was starting out a while back. :)

Hair for V4 -

http://www.sharecg.com/v/36166/gallery/Poser/Valens-Hair-For-V4/A4 (There are loads of expansions for this on sharecg)

http://www.sharecg.com/pf/full_uploads.php?pf_user_name=mylochka (Gallery is loaded with hair)

http://www.outoftouch.de/OOT/freebies/index.html (Three free for V4 here, WASG, Flexy Hair and Jingle Bells Hair)

 

As was already mentioned, Reciecup does some of the best african skins for V4 the freestuff for them is at:

http://rendercandy.com/index.php/cPath/25?osCsid=a91ae6e07c9fa9b1c8058a5aa1af5f52

Asian

http://www.sharecg.com/v/28420/Poser/Akina-for-Daz-A4-and-morphs++

http://www.renderosity.com/mod/freestuff/details.php?item_id=43393

 

Hispanic/Italian

http://www.sharecg.com/v/29483/Poser/Francisca-for-V4.2

http://www.renderosity.com/mod/freestuff/details.php?item_id=47397

 

Very Fair/Redhead

http://www.sharecg.com/v/33110/Poser/Colleen

 

Given a little time I can find more if you need any.

As has been mentioned, search sharecg and the free stuff here, both are treasure troves if you go digging.