I myself have not modded mine yet, but you could get started with some aftermarket wheels, a new grill, and maybe some HIDs. Not that many accessories I am aware of, but IMO the Malibu are well equipped as is.
What you looking to do? I have done wheels, tires, painted calipers, tint, added a 3.6 emblem and removed the Malibu emblem, removed the GM emblems, and I have a spoiler on order. Plus some other stuff I'm sure I forgot....
I got the wood dash overlay, tint, talking back-up system, LEDs for taillights, express up/down on the other 3 windows, 3rd brake light flasher, and turn indicators inside the exterior mirrors. I have more mods planned.
I am not realy sure what I like to do yet.....My 2010 LTZ came pretty well equipped. I think it already has LEDs..I like the idea of turn indicators inside the exterior mirrors... I like the stock wheels (for now). I would like to add a spoiler.........painted calipers sounds good too.
Are there any good web sites that have a lot of aftermarket parts to look at?