Jantje:
However there are currently no good (affordable?) simulators.
Jantje, have you tried this Simulator. There are two versions - a free version code limited to 100 lines and with a 30s delay on opening a sketch (increments by 1 each time a new sketch is opened) or an unlimited version for $6.99. We have had a lots of downloads Of the Free Version and around 10% choose to upgrade to the Pro Version. We have added a lot of features but there is still lots to do - such as adding custom libraries, structures and pointers.
With LCD, we have a lot of support for this and can run all the Arduino LCD Examples. The only issues here are support for 4line LCDs, accurate representation of 128 byte Hd44780 (or compatible) memory, and CGRAM. There should be some examples of LCD simulation on our Youtube videos.
Building a Simulator is very hard work and if we knew how much effort it would take, we probably wouldn't have started but there was little else around. Converting the Simulator to an Emulator could reasonably simple, if the Arduino compiler could add a simple getchar() routine between source lines, but this is more a question for the Arduino team. I am sure there will be an Arduino Emulator soon, probably sooner if more people request this.
Anyway, let us know if you want to collaborate. We were thinking of maybe adding some COM routines so that another program (such as a Shield Emulator) could receive Arduino output data in SPI,Wire,Ethernet,Serial, LCD or other interface. We have also been asked if a Simulator.dll is possible so that the Simulator can be externally extended.