I keep getting storage errors but I have plenty of free space, what is safe to remove from internal storage?
If you already have APP2SD and it says there's no app to move then there's no more app to move. I get this problem also when my I update and install new apps. I assume you are not rooted so you have less options. The only things you can do are:


Clear cache (install cache cleaner app)
Clear data of non-critical apps like Browser, Games, etc. (Manage Applications > Select Application > Clear Data)
Uninstall apps you rarely use, install them only when needed (e.g., I rarely Skype on my phone so I just uninstalled it)
Try a hack which will extend/squeeze the capability of APP2SD: http://www.bongizmo.com/blog/moving-all-android-apps-to-sdcard-apps2sd-froyo/ (this works well if you are rooted, if not there's still a few apps it can move).