I was looking for just such a tank bag. I originally thought that since I mostly wanted it to contain electronic goodies that I could live with a very small bag, and got the SW Motech / Bags Connection "Daypack". I love the EVO tank ring connection and the fact that the bag is semi-rigid and stays in shape even when empty.
But, after living with that one for about a year I decided to supersize the Bags Connection up to their City EVO bag. It is narrower at the front, which makes it so it doesn't foul on the handlebar switch gear even with Heli Risers on the bars, but has plenty of room inside for electronic / electrical gear and still carry a mess of other stuff, including a good sized camera (which is what prompted the upgrade). Crackberry cell phone is just sitting on the top of the RD in this pic ( I was uploading tapatalk pictures for a TOR this morning)
I got some extra lower tank rings for my V-strom and my son's VFR and can now swap the City back and forth between the FJR and 'strom and give the Daypack to my son for the VFR where it is more at home size wise.
In these pics you can see that I've also mounted a RAM magnetic "Power Plate" for the radar detector on the lids of the two Bags Connection bags. Having the RD on top of the bag is perfect. The wire runs are shorter and when it rains I can cover both the bag and RD with the bag rain cover. It is causing some light sagging on my City bag, but I'll re-enforce that with some semi rigid plastic material soon and eliminate that little foible soon enough.
The Bags Connection stuff isn't cheap, but I like them enough to recommend spending the extra coin on them. And that means a lot coming from a tight wad frugal Yankee guy like myself.