My 4 cents worth
To summarize and add to these posts:
1. Shimano Ultegra "brifters" will not work with V-brakes without a travel agent adapter. Neither will SRAM's new "brifters".
2. Canti-lever brakes will work with Shimano & SRAM brifters with no adapter needed and adequate stopping power. I'm not sure what one post meant by matching the canti brake type with the frame and wheels you are using. If you are using the correct wheel size for the frame's purpose (ie, 26" wheel for an MTB, 700c wheel for a road, cyclocross, etc), about any canti brake model will work, assuming the manufacturer welded the brake studs in the correct place. I've used a variety of canti brakes on a variety of frames and wheels. Canti's have a lot of adjustability so you can almost always make it work.
3. Cantis vs. vbrakes. Canti brakes have good stopping power; v-brakes have better stopping power. Older cantis had pads that were difficult to adjust, but newer cantis like the tektros use the same pad system as most v-brakes, so pad alignment is far easier on cantis that use v-brake type pads. Trying to match v-brakes with shimano or SRAM brifters will make setup and adjustment more complicated because you will need to use a travel agent adapter. I would tend to avoid the adapters and just go with cantis.
4. Disc brakes: Only AVIDs road version of the mechanical disc brakes will work with shimano or sram brifters. And even then, some people like to use a travel agent adapter for better pad-rotor clearance and better braking power with the brifter and road-disc brake combination. I've used Avids road disc brakes with non-brifter brake levers, and no adapter, and I will say that there are a lot of adjustment hassles. The levers will pull a long way to get decent braking power, and that is with the pads adjusted very close to the rotor, so that you could get some annoying rotor rub issues. A brifter with a travel agent with AVIDs mtb version of the mechanical disc brake might work, but with the same finnicky adjustment issues. Also, disc brakes are heavier than v or canti brakes. Those calipers are not light, and the rotors add some weight too (as well as beefier disc hubs).
5. The TREK Portland: Bike lust. OK, I haven't ridden this bike, but it looks to me like Trek got it right. They use Avid mechanical disc brakes with brifters (and no adapters), but the beauty of Trek's design is that they put the disc brake between the seatstay and chainstay, not on the top/back of the seat stay. So there are no complications or hassles with installing any rack you want. This would be one versatile disc-equipped ride!
6. Brifters vs bar-ends: I like the bar-ends. Cheaper initially, less complicated, lighter, and will outlast the brifters. They won't let you down, and even if they do, you can always switch them to friction mode and still have all your gears. Bar-ends let you trim the front derailleur for chain rub (although Shimano's new brifters are getting better at that, they still aren't as good as a friction shifter for the front derailleur IMO.) Downside to bar-ends is that you have to move your hands away from the brakes to shift, and some people don't like that. Doesn't bother me; actually moving your hands around reduces numbness.
Rich