For wood, I've found a 10.8v twin set to be perfect for DIY - loft boarding, shed building etc. YMMV, but I've a mains drill for masonry, so just dig that out if I need a bit more grunt.
An 18v combi will be better for masonry/metal, but heavier and you'll need to change bits if drilling pilot holes, then driving screws. With a twin set you can have both ready to go. Obviously you can get an 18v twin pack, but these are more expensive usually.
I've a makita set which comes with a 10.8v combi (though it's slow work for masonry, it's ok if you've only a couple of holes to do - ie a shelf) and impact driver. This range has been updated I believe.
The hitachi set is on offer at screwfix and looks a good buy, though I've not used it before, the 18v range gets a good write up.
http://www.screwfix.com/p/hitachi-k...-cordless-twin-pack-drill-impact-driver/57847
If you look around, the Makita, Bosch and Dewalt sets are normally sub £150 if of interest.
One other thing to look out for is the price of replacement batteries - may seem a small thing if you go through drills regularly, but I can see the batteries being the biggest weakness for a diyer and it would be a shame to throw away a good as the batteries are uneconomically expensive to replace.