Here's a link about a few types:
http://growhotpeppers.com/jalapeno-pepper-varieties/
Jalaro is the yellow. I haven't tried it. I have had the purple, and wasn't that impressed. I am going to try Biker Billy for the first time next summer. Mucho Nacho is huge; they get bigger than the 4" stated in that article, more like 4-6". Similar to Mucho Nacho, there are a lot of hybrids that grow huge peppers. I've seen a lot of 6" jalapenos in the grocery store.
Weather conditions, especially rainfall, determine the heat level. I have had jalapenos taste like green bell peppers if there is a lot of rain.