I guess I'm at bit biased since we made this app, but I really like the Team Portal iPhone app. Give it a try yourself together with your free SharePoint 2010 account.
Some of the current features:
- View and open your collaboration sites and sub sites
- Manage your favorite sites
- Open documents from your sites, share documents by link or attachment
- Flip horizontal for full screen view of any content
- Activity Dashboard
- Task lists (your tasks, overdue, all tasks)
- People list showing online and offline site members
- Call or e-mail your site members
- Choice to remember/forget your username and password
- Choose your default opening menu in this app