Web Browser: The N900 has the best mobile browser I've ever used (its built on firefox technology). Not only does it support full flash (9.4) but it renders page beautifully on the 800x480 resolution screen.
Camera: The little bugger packs a 5.8 mega pixel camera with an awesome flash. It takes both high resolution photos as well as decent quality video.
Music Player: The N900 has 32gigs of internal flash memory along with a slot for a mircoSD card that will take up to additional gigs - it holds a lot of media. In addition to this because of the full flash support I often stream internet radio on my N900 - as if this was not enough the little computer also packs a FM radio receiver/transmitter.
Flash Light: Just like a few other smart phones the N900 has an application that gives you a white screen to use as a white light. In addition if this is not enough to see by it also has an option to toggle the camera flash on as a light (its super bright!)
Video Player: Little bugger also does video out via a set of included RCA cables. The media player supports a wide slew of codecs as well, I watch movies off the little guy.
Gaming: Been rocking my Poke'mon lately. N900 has a GB, GBA, and a few other emulators for playing your favorite old school games on. In addition to this the N900 has full 3D support (and bounce evolution is super addicting...)
Phone: At the end of the day I sometimes forget my new toy also makes and takes phone calls. (And sends piles of text messages)
Calculator: My favorite CAS works wonderfully on my N900 fully - it makes a great little calculator.
Terminal: God I love cracking out commands in terminal. Lastly, I've been using apt-get to install applications on my tiny computer and sshing into my remote server.
All in all I am quite enjoying my latest toy and new software packages are being developed for it every day that only expand its usability further (there are currently packages in testing that turn it into a Wii-Mote and/or a PS3 controller). Heres to hoping 2010 brings many fun new toys!