App Suggestions: To me the most important are netcounter (counts data usage) and APNdroid (disables wifi/3G). I find the device to be data hungry and these ensure I stay within my contract limit of 500mb.

 

More important than any app I could ever suggest is my one piece of advice: Learn to use the forum correctly and search

(You'll find better information that way than if I just told you which apps to get since I could be misinformed - but even so I would get Quicksettings, Nesoid, Wiimotecontroller, MixZing, Documents to go, SIPagent, PDAnet, Shazaam )

 

Adding to what ap3604 said. We can also be biased For a type of app you're looking for, there will be at least 3 really good ones, you just need to do what everyone here did, search, play around with the apps, read reviews and then see which one you like.

This is the first stop I went to when I ordered my N1: http://androidforums.com/android-applications/1183-favorite-app-so-far.html

 

mypod - for podcasts
dolphin browser
pkt auctions - for ebay
0870
aim
anypost - for ping.fm
documents to go - word/excel/powerpoint/pdf office type thing
electrum
fxcamera
gentle alarm clock
google sky maps
launcher pro
layar
meridian pioneer - best media player as has FLAC support
lol sites
seesmic- for twitter
swype
sportypal
where's my droid

 

Honestly, its all personal opinion. Whatever apps I happen to like, you might hate and vice versa, and thats what makes android great, its personalization capabilities. I would take a gander at the thread for what people's homescreens look like. You might find some stuff in there you like, and can get some great ideas on what to get and how to set it all up.

http://androidforums.com/nexus-one/37620-post-your-nexus-one-home-screens.html