(in no particular order)

• Gravity (the Bentley of Symbian social networking apps—if you’re serious about Twitter and Facebook on your Nokia “smartphone”, you need this!)
• Symbian Podcatcher (until Nokia ports its old podcast app to Symbian^3, this is a must-have if you want podcasts on your N8)
• Pixelpipe Share Online (Ovi Store link) (if you’re serious about taking photos/videos on your N8, and uploading them to Flickr, YouTube, Facebook, etc., this is a must)
• Nokia Big Screen (currently in beta, but a real boon if viewing photos/videos on an HD TV, over the N8’s HDMI connection—even works with a Wiimote!)
• Skype (OK, it’s currently audio only—no video—but still very useful, along with the SIP VoIP settings app (for another Internet phone service like Sipgate))
• Nokia Battery Monitor (immense improvement on the built-in battery gauge; worth it for the homescreen widget alone)
• ComingNext (the calendar homescreen widget the N8 should have shipped with)
• WordPress for Nokia (very handy if you run a WordPress-based blog)
• Galaxy On Fire (3D space shoot-’em-up; great to show off, especially on a big TV via HDMI!)
• Angry Birds (oh come on, do I need a reason? 😉 )