Use it to emulate games systems, build it into a portable form factor (it only takes 5 volts so it is readily possible and has been done before on the original Pi), use it to control a robot, make a TV smart without Samsung add injections or build it into the dashboard of your car. Whatever you want to do basically. It is a very handy piece of kit and can attach to more modules than you could wave a stick at. It is down to you and your imagination. Have fun.
Ima jump in here for ideas as well. I just picked up the pi 2 from microcenter a couple days ago :)
Right now, I just moved the microsd from my old pi to the new one which is running a mumble server and a DDNS client.
In the past I have done all kinds of stuff with my PI model B. the most fun one that I did was write a python script to create a time-lapse video using PI camera you can get for about 30 bucks. I plugged it into a power bank and stuck it on top of a large truck at a football tailgate and got a pretty cool vid out of it.
I have also tried out raspBMC, which wont be supported for the pi 2, but they are working on an alternative for it.
I also used it as a torrent server to download/upload torrents without having to keep my pc running all night. I connected it as a network drive using SAMBA and ran my private internet access vpn on it for security/privacy from my isp crapcast.
The skys the limit with these things. Hope others will add their projects as well. The next thing i'm going to try is to run limelight on my pi to stream games from my PC to my TV in the next room :)
One cool thing I can think of (though it'll be a bit pricey) is controlling model trains with it. I've got a Linux laptop doing that using a Digitrax DCC system and JMRI, and its the best thing I've ever seen for model train control. The Pi 1 was a bit too sluggish to run JMRI but the 2 shouldn't have any issues. If you want tips on setup I'm happy to help.
You can also use it as an arcade, but the 1 could do that so I didn't figure that was very creative :P
Currently i have mine using Deluge to Automatically download torrents which is supplied via a rss feed from showrss.com and they are then transfered to a pc via ftp. it works pretty well at the moment, but the only issue is i cant save to an external usb for some unknown reason,I think its something to do with permissions still investigating. but the next project might be kind of a steam box type of thing for in home streaming. But a definite project will be a "smart" bed side able with voice commands ect. i will probs do a build log for that when it comes around. Well thats what i'm doing with mine for far, any feed back is much appreciated.