My Sugestions

Tab chats
Updated Emotions (the msn ones have got to go....)
Better vista intergration with Aero skin
Better Yahoo intergration
More features such as the ones found in the messenger plus! pack
Improved Formatting tools
Get rid of the Winks. they are too damn anoying and to childish
ReDisign the contact list. Ditch the tabs on the side, along with the ads
and have a nice clean, slim user interface
Show a small pop up window displaying a list of your off line IMs
Seprate screen for webcam viewing
Global Display pic, name and personal quote feature. - Log in to any pc and
have your personal prefaces there.
New Sounds-Less anoying nudge
Have an option to turn off nudges
Also have an option to trun off certin areas of the convo.
for contact list, have an option to change the size of the contacts. Slide
drager, such as the one found in the explorer window in vista.
Don't force people to join other live services.
Intergration with Windows Live mail
All extra packs should be part of the windows live galery and should be FREE.

Thats all I can think of for now, If I find anymore i'll post them