AIM works well enough. I run games on it.
Typing //roll uses the default numbers, two six-sided. Just using //roll-diceX will also default to six sides but still roll X dice (up to 15, annoying when you have high-reaction surprise tests or power-adepts). I find it works best to copy-paste "//roll-dice" for whenever you need it and just stick a number in. Finally, rolling most dice in the chat can make the players paranoid (always fun) when you don't tell them why you're doing it, but if you don't want to bring real dice to your computer desk, AIM will let you have two chats open at once, and you can do hidden rolls in there.
Running online also helps with the decker problem. You can run the decking half of the game in an IM or Private Message. Same goes for players who separate from the main group.
Edit: And if you can read German or find a translator, he's an RPG chat program with a mapping ability built in:
Pen & Paper