OK, this is a tricky one. I don't have a formal list of gaming axioms, but if I did two of them would be:
* This is a group activity, it is not any one person's game
* The players are always less invested in the game than the DM
Sadly, your position is such that the two axioms are in conflict. This is almost like one of Asimov's robot stories where the robot is in conflict with the 2nd and 3rd law of robotics so it wanders off and makes milkshakes all day long or something like that.
Basically, what I'm saying is that you might be fighting an uphill battle on this one and you may have more fun if you just ask the players if anyone else wants to DM. However, let's try to be more optimistic.
Do not play Call of Cuthullu. You can work Cuthullu into your fantasy game if you like, but playing a game where everyone is going to die or go insane is not a fun transition to the world of modern era roleplay.
Star Wars could be very cool IF the players are into Star Wars. Be careful though! If you have a Star Wars nut in your group he'll flip out if you so much as change the color of Darth Maul's lightsaber from red to beige. If the players are interested, let them pick the era they want to play in (pre-Empire, Galactic Cvil War, or post-Empire). Don't use the movie heros in your game. This is supposed to be about the PCs not that Skywalker kid.
d20 Modern this is free. The SRD is free. This is the big selling point. Free. Emphasize that. No books to buy. Free. I'm running an off-and-on Urban Arcana game and the players seem to like it. It has less of a "feel" than the other two settings though. It also is very deadly. People used to high fantasy may not like that.
Above all: Prepare, prepare, prepare. You want the players to like the game and it really is an effort on their part because if they agree, they're accomidating you. That's nice of them. So prepare your games and plan out your encounters.
Hope this helps.