You can now buy halogen conversion kits to replace your old sealed beam units. This gives you a choice over the bulbs you can fit, and therefore how much light you get coming out of them.
I recently changed my old Land Rover sealed beam units for halogens, and the difference was amazing. Now if a light blows, then all you have to do is change the bulb, and not the whole light unit.
One word of warning though about halogen conversions, they can draw more current than the old Land Rover units, so make sure your wiring is up to it, and if need be, fit a relay kit as well.
Handy tip: Wipe your headlight lens with Rain-X and any mud or water will simply bead off the lens keeping them clearer for longer!
Roof mounted lights
For off road purposes they are useful to have mounted on the roof, so they are away from mud and will stay cleaner for longer - and therefore brighter. This will also protect them from flying stones etc - but in many countries it is illegal to use roof mounted lights on public highways.