A staple of many space marine lists even before the advent of the Contemptor class dreadnought. And with good reason: these guys can be configured in many ways for a variety of roles. To be honest, I'd be a lot more tempted to field contemptors than the regular dreadnoughts since the price increase is very worth while. That said, the regular dreadnoughts are cheaper and have viable builds. Multiple talons of these dreadnoughts will cause headaches and they're fluffy for Iron Hands, Iron Warriors, and so forth.
One key item to remember here is that one can field up to 3 in a single talon. Although they're deployed together, they are then treated as individual units from there on.
Here are a build ideas. I'm only looking at individual dreadnoughts here, but there is clearly room to add in other dreadnoughts (or similar or different builds) to aid the rest of the talon.
Dreadnought, 2 close combat weapons with in build heavy flamers, havoc launcher (160 points)
A classic close combat build with 2 weapons and heavy flamers for taking out large blobs of infantry. Add on a havoc launcher just because its great. Add on a drop pod if you can and go stomping.
Dreadnought, 2 close combat weapons with built in plasma blasters, havoc launcher (180 points)
Getting a bit pricey, but replace the heavy flamers with plasma blasters and then go hunt down some heavier infantry.
Dreadnought, 2 twin linked missile launchers, havoc launcher (165 points)
Plenty of blast templates and potential to hurt light tanks. Sit around and pick your targets to take down. An excellent support build.
Dreadnought, 2 twin linked auto cannons (140 points)
Dreadnought, Multi melta, close combat weapon with in built melta gun (140 points)
Place in a drop pod and go tank hunting.
Dreadnought, siege-wrecker with in built heavy flamer, Flamestorm cannon (150 points)
A mixed purposed dreadnought. Crack open a fort and fry the contents. Beef up the armour if you feel you need to with extra armour or armoured ceramite.
Dreadnought, close combat weapon with in built twin linked bolted, plasma cannon (135 points)
Cheap. Cheerful. Effective. And one of my favourite ways to configure multi-purpose dreadnoughts. Several of these will cause headaches.