I use to do the Blackberry Bold and iTouch 4 combo. It was a nice compliment to my, at the time, practically gameless Blackberry. Having a larger and clearer screen for watching videos and browsing the web was great too. I've since traded in my Blackberry for an Android device and now use it with my iTouch. Sadly, my iPod hasn't seen much use after my transition to Android. Unless I'm trying to create music on a handheld, I haven't really found anything my iTouch does better than Android. The advanced equalizers with compression make it a superior device for listening to music, Flash and a faster processor make browsing the web quite a bit more enjoyable, and most of the major iOS games get ported to Android as well.
It's still a great device and miles ahead of Blackberry's OS (something I never thought I'd be caught saying.. I was quite a Crackberry head).
My advice if you're looking for a BB companion.. Go to a BestBuy or comparable store and get a little hands on time with an iPod touch to see if it's really what you're looking for. Then check out a comparably priced Android tablet. It never hurts to try out all the options you have, right?