Show/Hide Fields
Installation
Copy the solution to the server and use stsadm or powershell to add solution to solution gallery.
Enabling
For the specific web application, enable the web application feature "SPC3 ShowHideFields Breadcrumb"
For the specific site collection, enable the site collection feature "SPC3 ShowHideFields"
Using
Navigate to any list or document library.
In v4 visual styles, a new ribbon tab called "Extended" will display.

In v3/v4 visual styles, a new action under list settings -> general settings will display.

Use the configuration screen to show/hide your fields.
Hidden fields will display in the list, but not be editable
ReadOnly but not Hidden fields will display in the list, but only the view forms will be editable.
Most of the forms use a nullable boolean (bool?), so a tri-state radio button is required.
Powershell
This can be done in powershell, but requires server access
$list = (Get-SPWeb "http://yoursite").Lists |? {$_.Title -eq "yourlist"}
$field = $list.Fields
"yourfield"$field.ShowInNewForm = $false
$field.ShowInEditForm = $false
$field.ShowInDisplayForm = $false
$field.Update()