Ok, so here's my list. Most of the things have already been cited, but I guess if people recognize some of their favorite apps in my list, maybe the rest might interest them as well.

In bold, the real life-changing apps. The list is in alphabetical order.

• AdBlock plus (removes ads from web pages)
• adflashblock-css (lets you chose if you want flash to be played on web pages)
• Auto-Complete editor (to remove annoying typos from the auto-complete dictionary
• BlueMaemo (to control your computer though bluetooth. Useful as media remote)
• CasualServices (to find stores and other services like dry cleaning around your location - works really well)
• Conboy (for general note-taking)
• Dorian (for e-book reading. I used to be a fan of FBreader, but this one has all the advantages of FB, and more !)
• Facebook plugin to share photos
• Flashlight
• Foreca Weather Widget (to know how to dress in the morning)
• Hermes (to get contact infos and avatars from facebook)
• Merge your duplicate contacts (to easily find and merge contacts entered twice)
• MGutenberg E-book Reader (because FBreader and Dorian's e-book downloading system doesn't work or doesn't exist, and MGutenberg's works flawlessly.)
• OpenSSH client and server (for geeks :-) )
• pygtkeditor (a really great editor to code some python scripts on your N900)
• recaller (for use as a dictaphone and to record your phone conversations)
• SeriesFinale (to keep track of what you saw and what's new on the air in all the series you are watching (and I watch a lot of them) )
• Shopper (for making your shopping list effectively)
• TouchSearch (search from your desktop directly to google/google maps mobile/imdb/wikipedia/etc (faster than opening a browser first)

That's it. I didn't list all the extra codecs and IM protocols.