1) I would like to see a bing radar overlay for bing maps, or at least an ap for it.
Here's an example of it.
2) Contact filtering by category. Live contacts supports categories, not sure why WP7 can't do it.
3) Sync to subscribed calendars.
4) Flickr integration similar to facebook so I don't have to use the flickr ap and my friends photos will show up on the photos page.
5) Some sort of facebook filtering so I don't have to have every single facebook friend contaminating my phone. Maybe the option to just sync categories like friends and family? ...or at least an option to set some people to ignore.
This is what I can come up with at the moment, I'm sure there will be more.