the dress code in ibiza is pretty much anything goes, but in general is more relaxed than at home !!! more Miami than NYC...
Pacha is the most glam/dressed up club and for DC10/Space/Bora Bora you would be OK even with bikini top/hotpants, little summer dress, or vests/shorts/flipflops for the boys!!! shades are essential though.
As its pretty hot, generally the less you wear the better, formal shirts and smarter trousers for guys are a definite no no in the clubs really, but a casual shirt would be ok for Pacha I guess (although my boyfriend only owns one shirt)
jeans are ok anywhere and shoes.... well there are hundreds of girlie threads on this site on that topic - search "shoes"!
barbie is the regular fashionista here, I am sure she will chip in at some point in this thread to give more info
the space website has galleries of the crowd and a really good video of last years opening and closing parties which you can see the style in anyway!!
have fun choosing your outfits!!!