Configure the firewall (q.v. the iChat configuration below)
System Prefs -> Security -> Firewall -> Allow Only Essential Services
Click the Advanced button and, check "Enable stealth mode."
If using "Set access for specific services and applications" to support iChat or other applications, remember to set these other applications to allow incoming connections:
Vine Server (for Evermore Remote)
Turn off BlueTooth
Run System Update, rebooting after each set of updates, until there are no more
Install iLife (if desired)
Run System Update to get iLife updates
Improve login security: System Preferences > Accounts > Login Options
Set automatic login disabled
Set "Display login window as" to "Name and password."
Show Restart, Sleep, and Shutdown buttons.
Do not show password hints.
Do not enable fast user switching
Set the date to display in the menu bar. Note that this can be accomplished from the System Preferences in the next Mac OS X release (Snow Leopard). From the command line (Terminal) type:
Note: I am not sure this is working correctly in Snow Leopard.
Check iChat settings (if you want to use iChat). Sometimes, iChat does not connect properly to AIM on the default port set by Apple.
Set the port in iChat Preferences > Accounts > Server Settings. Ports to try include 443 and 5190.
Video chat is often even more challenging to get working and, may require changes to the firewall settings. Specifically (in Mac OS X 10.4 or later), open TCP ports:
5190, 5220, 5222, 5223 and, 5298
... and UDP ports:
5060, 5190, 5297, 5298, 5353, 5678, 16384-16403
In Mac OS X 10.5, you set the firewall to "Set access for specific services and applications," add iChat and, set it to "Allow incoming connections."
In OnyX Parameters > Login, "enable show message in the login window": If found, please call 623-934-9010.
(Optional) TinkerTool - allows you to tweak various settings (GUI behaviors, font settings, etc.). I am installing this but, not changing anything currently.
AppleJack - This is nice to have installed if there is a disk or permissions problem. It can be run from a shell in single-user mode to run the standard battery of repairs.
TotalFinder adds tabbed browsing to Finder, which is useful, particularly if you are not using PathFinder. Update: it turns out this is only free during development release. After that, it will be $15 and, you might as well buy PathFinder.