"Gotta Haves" - for Droid users at least --
1. Beautiful Home - great looking, quick access to alarm clock, weather, calendar (paid, but well worth it)
2. Helix Launcher - alternate to default home/launcher - more home screens, dock bar, jump to screen ... very cool (free)
3. Lookout - malware scanner, online backup, and lost/stolen phone recovery (free)
4. Advanced Task Killer - keeps my Droid running smoothly (free version)
5. LastPass for Android - cloud-based encrypted password vault and "filler-inner" (paid)
6. Dolphin Browser - improvement over default browser (free)
7. Astro - file manager and app installer (free)
8. Evernote - my memory in the cloud (free version)
9. Car Home - Turn-by-turn directions and maps (free)
10. Countdown Timer - simple, often used, and ... (free)
11. Pandora - internet music tailored for you (free)
12. Aldiko - ebook reader (free version)
13. Barcode Scanner (free)
14. System Panel - performance info (free)
15. 3D Level - surprising how often this comes in handy when you always have one with you (free)
16. Droid Dictionary - also links to thesaurus entries (free)
17. Droid 411 - directory assistance (free)
18. DroidLight by Mototols -LED flashlight for Droid (free)
And I could go on and on ... soooo many great apps, and mostly free! Android rocks!