I use Plaxo Premium's de-duper which is free for me because im a comcast customer. but I just googled this for you and hope this helps you because this is a free solution.
http://www.rimmkaufman.com/rkgblog/2...look-contacts/
"Here’s a free, relatively fast, hands-on deduping approach that worked for me: export contacts to Excel, create a signature field indicating uniqueness, sort and dedupe on the signature field, then re-import the cleaned contacts into Outlook. Here’s a detailed step-by-step recipe
1. Back up your .OST or .PST file, in case you make a mistake.
2. Make a temporary subfolder under your contacts. I named it “Stash”.
In Outlook2007: Go >> FolderList >> Right Click on ‘Contacts’, select ‘New Folder’.
3. Drag all your contacts, duplicates and all, into Stash.
4. If on Exchange, Send/Receive (F9) to sync local with the server.
5. Export the Stash contacts folder in Excel.
In Outlook2007: File >> Import and Export >> Export To File >> MS Excel 97-2003 >> Stash.
6. Open the export file in Excel.
7. Insert three new blank columns of the far left, so the first column of data now lives in column D.
In Excel2007: Home >> Insert Cells >> Insert Column.
8. Decide what constitutes a duplicate record in your world.
9. In Cell C2, insert a formula concatenating together the fields which define dupeness.
1. For lastname-phone dupes, enter (on my version of Outlook):
=CONCATENATE(G,AI,AM)
2. For full dupes, enter
=CONCATENATE(D1,E1,F1,G1,H1,I1,J1,
K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,w1,x1,y1,
z1, AI1, AM1, BI1)
The columns actually go over to CP, but I got lazy typing all that in. An Excel function to concatenate ranges would have helped.
10. Copy down the C2 formula down to every row in your sheet in Column C.
11. Sort your sheet, rows 2 to the bottom, by Column C. This sorts your dupes alongside their twins.
Data >> Sort
12. Create dupe formula in Cell B2
=IF(c3=c2, "Dupe", "Unique")
and then copy it down to all cells in Column B.
13. Copy all of Column B, then “paste values” into Column A.
On Excel2007: Home >> Paste >> Paste Special >> Values
14. Sort your sheet again, again from Row 2 downward, this time on Column A descending. This sends the dupes to the bottom and the uniques to the top.
15. Highlight all the dupe rows at the bottom of the sheet and delete them. Au revoir!
16. Delete columns A, B, and C.
17. Save this new sheet with a new name.
18. Import the sheet back into Outlook, typically into your root Contact folder.
In Outlook 2007: File >> Import and Export >> Import From Another Program Or File >> MS-Excel 97-2003
19. Voilà! Deduped contacts. Check that everything went OK. Delete the Stash folder when you’re confident.
20. If something goes wrong, Microsoft’s scanpst.exe or scanost.exe may be able to help repair your OST or PST file. (But you made a backup in step 1, yes?) "