Fantasy Ferret is pretty solid. Like the above poster stated it isn't the prettiest WP7 app but at least it's functional. It absolutely blows my mind ESPN doesn't have an app for Fantasy yet. I mean they have it on Blackberry for the love of God! No Windows love?
Check out fantasy football news. Free app, has news from fantasy football today, fantasy mastermind, yahoo, espn, sporting news, NFL.com, roto, fantasy shark, fantasy champ, ADP football calculator, podcenter, videos and more.
I use Fantasy Football Monster. It lets you use your ESPN and Yahoo. You can add/drop players, manage rosters and watch matchups, see game box scores for games, news, injuries, headlines, standings, etc. It's pretty comprehensive.