kinch

Starbucks Langsuan is the logical choice. Provided not university exam time or Sunday afternoons, it's reasonably quiet and possible to get seats. Londoner Pub is OK too at non-peak times, although discerning people prefer Bull's Head in 33/1. One thing to be said for the Suk 33 area is that there's lots of good stuff to eat (ramen, no less) in 33/1.

Of course there's always Cafe Ubuntu in Soi Saladaeng :).