I really like programming simple things, like solutions for Project Euler, where you can concentrate, write an algorithm, instantly execute, test, verify and change the program until it works. Even for bigger projects I feel I can maintain flow and be very productive as long as I can stay in one IDE (e.g. Eclipse) and everything compiles and starts fast, for example, if it is a Swing GUI.
I know this questions may sound subjective but it is an important issue for me and I think it can benefit many others as well.
P.S.: What I am looking for is a solution to web development which allows staying in one IDE and which allows testing and executing without long waiting for long compiles, deploys, ect.