As of today, July 2009, there are a number of ASA 100 speed films on the market. Kodak has their Tmax100 and Plus-X, Ilford has their FP and Delta varieties, and Fuji offers Acros. I have tried them all but keep coming back to Acros as my main B&W film. The two most outstanding characteristics this film displays are low-grain and excellent shadow/highlight range - dynamic range - which lets the film keep detail in the darker, shadowed areas without the brighter areas becoming overexposed blobs. This is a fine balancing act and this film does a great job of it. I especially recommend developing this film in Kodak's Xtol developer, with a 1+3 dilution. The film's sharpness is superb with this combination.
The biggest drawback to this film is price. It usually sells for more than the Kodak or Ilford offerings, but it's worth the extra cost.