Finally, a modern ruleset for 4e!
I liked d20 Modern well enough, I really did. It introduced certain elements like Damage Threshold (making guns very scary things even when the PCs had buckets of HP), heroes based directly off of a particular stat, and easy multiclassing that gelled well.
Now we have Dias Ex Machina's offering, making the D&D 4th Edition game system viable with firearms, grenades, even up to futuristic robots, nanomachines and laser/plasma weapons. You choose from a Ladder which helps offset the need for enchanted gear by using enhancement bonuses granted every few levels, then you select a Class. There's quite a few to choose from, and while some Ladder/Class combinations are more optimal when paired together, there's really no useless selection to make (with the understanding you may have to strain your attributes a bit).
The system can do anything from Civil War to Wild West to Space Opera. It's not a standalone, instead a supplement to the WotC 4e books. Well worth the price of admission, I give this one 5 stars.
[5 of 5 Stars!]