Mandatory to have: UGS Web Part collection (thx to Mark)
Thx to Mark Harrison
UGS contains one of the nicest web part collections I've seen:
Breadcrumbs - Fairly standard.
Connected Page Viewer - More IFrame attributes than the Page Viewer, and works with connected web parts.
Event Rollup - Aggregate calendars from subsites. Nifty!
Flash Movie - Just what it says, clean implementation.
Google Search - Displays results in-place, and can be configured to search a particular site.
Outl2TccSyncer - Much potential, the goal is to synchronise Outlook and SharePoint calendars.
Poll - Looks more like what you're used to than the built-in survey.
QuickTime Movie - Just what it says, clean implementation.
RateThisPage - Short and sweet, again more like what you're used to.
Site Navigation - Clean display, and many display options (from root, from child, etc.)
User Alerts - Lets an administer add, remove or change alerts for any site user. One way to push alerts rather than wait for users to subscribe.
Welcome - Display personalised welcome messages.
What's new - A concise list of New items on a team site.
World Time - If your users work in different time zones, it helps to show clocks for each.