My old touratwat tank bag has come to the end of it's life, with zip pulls broken and the base zip not zipping and coming apart from the seams. It's done a good job, but i've never been happy with its lack of waterproofness.
Following a bit of research. where I was looking strongly at the SW Motech Trial Bag system, I then had another gander and found Enduristan Bags from Germany.
They come in different sizes with really good sized map pockets and, although they lack the SW Motet's tank ring, they do have a harness that unclips, so you can fold the bag backwards and fill up easily.
For me, the build quality, price, waterproofness - including the map holder and interior storage makes this bag way better than the Motech Trial.
SW Motet's Evo bags also have a natty 12v attachment, but that also costs. My Enduristan has waterproof ports for power cable to pass through, so I bought a motorcycle wiring harness and camera battery charger for a lot less money than going the SW route.

If you're on the lookout for a great, waterproof, tank bag that costs less than the competition, is better made than the competition, you can get them from Gabriel at Zen Overland.