I bought the "Pro tool kit" that this site offers. I also found that although the kit came with 45 tips, i only use 3 on my iphone 4. They are the Pentalobe #2(smallest in the kit), the Philips PH000(also the smallest), and the Straight 2.5(5th smallest).
Here is my take on the quality of these items.
Pentalobe:#2 Seemed to small the first time I used it, but the next size(5) was decidedly to large to even begin to fit. So I had to use the #2. Soon the tip rounded off, due to the sloppy fit. However since the bit is tapered I decided to dress the tip with a file, and was able to make this one fit nearly perfectly. Since the material seemed a bit soft(it will easily round off again so be gentle, making sure the back is seated rather than trying to use the screws to pull the back cover into position when buttoning it up) I left it a little small so I could redress it again if necessary.
Philips:#000 For me this one is the best. It fits every screw I have attempted to remove, and I have removed them all. It is just sharp enough,(the#00 wont go in any of the small screws, and doesn't fit the rest very well either) and it is holding up well.
Straight:#2.5 These I had a problem with. It seems that the different number designations(1.0,1.3,1.5,2.0,2.5,3.0,3.5,and 4.0) indicate the "Width" of the blade, but there seems to be no rhyme or reason to the "Thickness" with only the 1.5 and lower being sharp enough to fit in the slots on those threaded hold down screws,(you know the 3 that you screw through the mobo that recieve the smaller philips screws for the battery hold down, the chargingdock cable, and the grounding antenna hold down at the top) the only problem is those ones are not wide enough, because of the threaded hole in the middle of the screw. the 2.5 is the perfect width but I had to, once again, breakout the files and dress a sharper tip onto it so those screws would accept it.
Apart from these minor difficulties, I love the kit. what with the 4 kinds of tweezers 3 metal prying tools,(these are quite sharp and perfect for prying up components with adhesive holding them down) and a plastic one that has a sharp tip just right for positioning the ribbons for the volume buttons and whatnot.
Lets face it, if you are a good tinker, its because you were first a good toolmaker, right?