As far as I am aware all of these give free follow links, if you know otherwise leave a comment below.
1 – http://slashdot.org
2 – http://digg.com
3 – http://technorati.com
4- http://www.furl.net
5 – http://www.backflip.com
6 – http://www.hugg.com
7 – http://www.mixx.com
8 – http://ma.gnolia.com
9 – http://www.connotea.org
10 – http://mystuff.ask.com
11 – http://www.reddit.com
12 – http://www.dzone.com
13 – http://www.folkd.com
14 – http://multiply.com
15 – http://www.searchles.com
16 – http://de.lirio.us
17 – http://www.dotnetkicks.com
18 – http://www.bloghop.com
19 – http://www.plime.com
20 – http://www.bibsonomy.org
21 – http://www.clipclip.org
22 – http://linkagogo.com
23 – http://www.spurl.net
24 – http://www.zlitt.com
25 – http://www.indianpad.com
26 – http://www.tumblr.com
27 – http://www.myvmarks.com
28 – http://www.listible.com
29 – http://www.bringr.com
30 – http://faves.com
31 – http://www.linkinn.com
32 – http://spotback.com
33 – http://www.mylinkvault.com
34 – http://my.xilinus.com
35 – http://linkatopia.com
36 – http://www.bumpzee.com
37 – http://www.bookmarktracker.com
38 – http://www.healthranker.com
39 – http://www.a1-webmarks.com
40 – http://www.wirefan.com
41 – http://www.bmaccess.net
42 – http://blogmarks.net
43 – http://www.diigo.com
44 – http://www.oyax.com
45 – http://socialogs.com
46 – http://www.contentpop.com
47 – http://www.pixelmo.com
48 – http://www.memfrag.com
49 – http://getigadget.com
50 – http://www.jumptags.com