Up to now I've exclusively used soft luggage (Wolfman bags) on my WR250R. Soft luggage is more forgiving of crashes and more accommodating of being stuffed with irregular-shaped objects than hard luggage, is lighter, and is generally easier to add/remove depending on what my trip plans consist of.
For our Continental Divide ride this summer, Jeff had mounted a simple top-box on his DR650 that proved to be very ergonomic and practical. Being much easier to access than a zippered soft-bag or even our backpacks, it became our riding trio's go-to spot for paper maps, sunscreen, and other frequently-accessed items. Jeff had also wired a USB port into the case, making it an excellent spot to securely recharge phones, Sena headsets, and other items that were awkward or not practical to charge another way. Also, the addition of a nifty Grid-it panel inside the lid had me totally sold on replicating the set-up. Jeff attached his panel by first clamping it to a board with mirror clips, then using 3M double-sided tape between the panel and lid. I'll probably do something similar.
Jeff's box was an inexpensive impact-resistant tool box from Princess Auto:
The model shown here is larger than the one Jeff and I bought (for some reason, Princess doesn't list ours on the web site), so it's best to check in-store, as there was a good selection of sizes. Mine cost around $60, but don't be fooled by the low price: it's truly a sturdy case that is moulded and assembled well, closes securely, and appears to seal well.
Since I already have a rack I made made from 6mm aluminum plate on my bike, it was just a matter of drilling and threading four holes to accept some mounting bolts inserted from inside the case. As I'd done for a RotoPax mount, I drilled holes to accept M6 HeliCoil inserts which provide more mechanical strength than tapping the aluminum directly for M6.
If you adopt a similar mounting method and box, be sure to check if there's a gap between the plastic and the rack, and fill it with a washer if there is. Also, be sure to use some beefy washers inside the case, and use thread-lock on the bolts.
Next, I'll be wiring in a USB port, probably moving the one from my handlebar which I rarely use anyway. I plan to incorporate a quick-connect plug for the power to the box, so that removing the box is easy and leaves a useable power point somewhere easily accessible on my bike.