I'm mainly interested in numerical tools. Boost has a good start (random, array, math, and rational libraries), but I'm hoping there will be much more in the future. I have also found several of boost's libraries (tuple, smart_ptr, call_traits, type_traits, integer, concept_check, test, timer, pool) useful to various degrees in my last project. (I wish the any and tokenizer libraries had been avaliable a year ago. :) )