Top 50 most played albums on iTunes So Far in 2010 (w/o artist duplicates - to be included the album had to have 80% of the songs with roughly the same amount of plays. ) I tend to alternate listing to full albums with listing to playlists, so that makes for some interesting differences. 

1) Iron Maiden - Live After Death 
2) Ra - From One
3) Bird3
4) Angie Aparo - For Stars and Moon
5) Enuff Z'nuff - Tweaked
6) Alice in Chains - Black Gives Way To Blue
7) Crowded House - Recurring Dream
8) Soul Asylum - Let Your Dim Light Shine
9) Collective Soul - Hints, Allegations and Things Left Unsaid
10) Guns N' Roses - Appetite for Destruction
11) Ozzy Osbourne - The Blizzard of Ozz
12) The Exies - Inertia
13) Donnie Vie - Extra Strength
14) Switchfoot - The Beautiful Letdown
15) The Offspring - Americana
16) The Soundtrack of Our Lives - Origin Vol 1
17) Rolling Stones - Forty Licks  
18) The Jimi Hendrix Experience - Electric Ladyland
19) Staind - 1996-2006: The Singles
20) Pearl Jam - Ten
21) Yummy - Elegante
22) W.A.S.P. - The Last Command
23) Prince - Purple Rain
24) Jughead
25) L.A. Guns
26) Beatles - Let It Be
27) Ramones - Weird Tales of the Ramones
28) Dio - Holy Diver
29) Third Eye Blind - Blue
30) Duran Duran - Wedding Album
31) Beach Boys - Pet Sounds
32) Fleetwood Mac - Rumours
33) Def Leppard - High 'N' Dry
34) Twelvehourmary - Blowing Over
35) Black Sabbath - Born Again
36) Cat Stevens - Tea for the Tillerman
37) Bangkok Five - Who's Gonna Take Us Alive
38) The Tories - Wonderful Life
39) Badlands
40) James Taylor - Greatest Hits
41) Riot - Narita 
42) Megadeth - Peace Sells
43) Kid Rock - Rock N Roll Jesus
44) Seal
45) Unified Theory
46) Shooter Jennings - Electric Rodeo
47) Harry Chapin - Greatest Stories Live
48) ELO - All Over The World
49) Linkin Park - Hybrid Theory
50) Redd Kross - Phaseshifter

I sorted my master iTunes list by play count to see what the top 50 were.

1) Metallica - Battery 
2) AC/DC - Highway To Hell 
3) Soul Asylum - Stand Up and Be Strong 
4) Bird3 - air crisp> 
5) Tonic - Ring Around Her Finger 
6) Ice T - Colors 
7) AC/DC - Shoot To Thrill 
8) Def Leppard - Women 
9) Little Big Town - Vapor 
10) Emerson Hart - When She Comes
11) Tonic - Believe Me
12) AC/DC - Rock and Roll Ain't Noise Pollution
13) Collective Soul - Untitled
14) Judas Priest - Locked In
15) Metallica - Master of Puppets
16) Dio - Caught in the Middle
17) Fall Out Boy - Dance, Dance
18) Metallica - Creeping Death
19) Apocalyptica - I'm Not Jesus
20) Guns N' Roses - Rocket Queen
21) Ra - Fallen Angels
22) The Cult - Rise
23) The Exies - Ugly
24) Metallica - Welcome Home (Sanitarium)
25) Def Leppard - Mirror, Mirror
26) Metallica - Fade To Black
27) Billy Idol - Dancing With Myself
28) Everlast - What It's Like
29) Collective Soul - I don't need any more friends
30) Beatles - Let it Be
31) Kid Rock - Blue Jeans and a Rosary
32) Mandy Moore - Cry
33) Metallica - Fight Fire With Fire
34) Guns N' Roses - Better
35) Alice in Chains - Your Decision
36) Metallica - For Whom The Bell Tolls
37) Alice Cooper - Billion Dollar Babies
37b) Crowed House - Don't Dream It's Over
38) David Bowie - Blue Jean
39) Ozzy Osbourne - Mr Crowley
40) AC/DC - Hells Bells 
41) Jughead - Halfway Home To Elvis
42) The Soundtrack of our Lives - Transcendental Suicide
43) Angie Aparo - Child You're The Revolution
44) Prince - When Doves Cry
45) Bird 3 - Indoor 
46) Staind - Outside
47) Angie Aparo - Suicide
48) Ra - Only
49) Jimmy Eat World - The Middle
50) Suicidal Tendencies - Hear Voices
 
This list only takes into account the plays since Dec when I did a clean install of windoz. Figure 2-3 hours a day for 3 and a half months. But to be honest I never thought of myself as a big Metallica fan but they ended up dominating with 7 out of the top 50 songs and some of who I thought were favorites didn't even make the song list until the 30s and 40s. I'll have to do this again in three months and see how much has changed since these results come mostly from playlist which I change up often.