As you may have noticed from the message at the top of msn groups pages, they are closing groups for good. I have checked out several sites to see what they are like, there will be things you like and don't like, depending on where you decide to settle. Here is the list I have so far.
Google Groups
You get 100mb of storage, can create pages in html format, can have chat, forums, blogs, messenger and email. There may be other things you can get for google. Can be made private or public
ning.com
You get 10mb of storage unless you pay for more which will also remove ads (no popups there and it's a small section of ads), you get a forum, music, video and other stuff depending on what you want in your group, you can have blogs. You can change your main page, which is what all your pages will look like and is in CSS format, not html. It also has rss feed ability, can be private or public, has a basic template you can use and manipulate
yuku.com
It's possibly the closes to msn groups you can get that I have located so far. You get forums, image uploads, format is in CSS but has design tools to help you, best check this page for more info on it...
http://www.yuku.com/home/yukucustomize/ it has chat, private messaging, video and rss feed ability, can be private or public
multiply.com
This site is currently updating their services due to the transfer of msn groups and help ease the situation. They have blogs and groups, are free, can upload images, have forums, CSS format not html, comes with templates that can be manipulated, though there are hundreds of free one's you can use.
Thats pretty much it for the moment and will let you know if there are others as I come across them.