I've got some basic 1.6" slicks for commuting on my mtb but I think something lighter and thinner would be better for higher mileage - 100 miles/day. But gotta be tough enough for the extra weight of panniers; I'm thinking something from Continental around 1.25".
i used schwalbe marathons in iceland for 6 weeks - super tough with good tread. barely got worn through the 6 weeks despite heavy load and non-tarmac roads (some were just finely raked soil as the roads get rebuilt each year in places).
i had 1.9s i think, but i'm sure they come thinner too. reasonably heavy though.
Schwalbe Marathon
Hmmm...was thinking of avoiding Marathons as a bit much for a week's riding on good roads; the ones I've seen are so heavy!
Heavy. But beautifully smooth.
http://www.allterraincycles.co.uk/product/111431.html
Never had any bother with these on my road bike
I used Specialized Nimbus (normal, not puncture resistant variety) on a 3000 mile fully loaded tour. Not a single puncture.
Another vote for Schwalbe Marathons. Don't worry about the weight - that's just the price you pay for their durability. Pump them up to 60-70psi for your road sections and they'll roll so well you won't notice any weight issues.
I have used the contis sport contact in 1.6 size Comes with a free innertube and a 1 yr puncture free guarantee. Can be inflated to over 100psi as well. Much recommended
Another vote for Conti Sport Contacts.
Schwalbe Marathons are fine if you are obsessed about punctures and don't mind a load of extra weight. But if you can live with the occasional puncture then go for something lighter.
Conti double fighter.
I'm glad the conti supporters have come along - thinking about Conti Sport Contacts in 1.3; I think they'll be big and tough enough for riding through Brittany and sticking to the roads...if I was getting more adventurous then Schwalbe would be the obvious candidate I'm sure.
I'm running Double Fighter IIs on my commuter hardtail. I got them to deal with unclasified lanes, mud, slimy surfaces etc and they work well but might be overkill for nice tarmac. Good country tyre though.