Arbo 1096 from Arbosil is the absolute business. One component, sticks very strongly to acrylic (and is designed and tested for that purpose, not just for glass). Easy to work with, relatively easy to clean, not too thick so it's easy to squeeze out. Pretty much everyone uses it as the main product for boat windows in the UK. I've been trying hard to find it in NZ but I can't. If anyone tracks it down here then please let me know. It's not only a really good product but cheap too! Only about $13 for a big cartridge of it.
If you need a decent quantity it might be worth ordering it from th