KA378R05
Vendor's Description:
The KA378R05 is a low-dropout voltage regulator from Fairchild Semiconductors. From the page, "Dropout voltage of KA378R05 is below 0.5V in full rated current(3A)". It does have a 4-pin layout, the fourth pin is "Disable". Just tie that pin to your supply line and it'll work fine.
Available at Mouser for $1.58, probably elsewhere too. I got mine as free samples from Fairchild, so you may find some that way too.

2009 July 01, added quickie schematic



@ Sat, 2009-07-04 05:22
I'm not going to update the
I'm not going to update the actual post, because I don't want this to bump onto the front page again ;)
I replaced the schematic with a (hopefully) better version. If it's hard to see, right-click and "View Image" (or whatever your browser calls it), should be a bit clearer that way.
I didn't find an Eagle library with this part in it (didn't look very hard either) so I tried making one. That's why the part looks... off. I'll likely update again if/when I learn more about making custom parts and footprints and stuff.
@ Fri, 2009-07-03 22:02
Yup.
@ Sat, 2009-07-04 01:11
Standard caps
@ Fri, 2009-07-03 18:48
No Polarized Caps?
@ Fri, 2009-07-03 19:58
Oops. Ya, I missed that
Oops. Ya, I missed that part. That's what I get for quickie diagrams... haha. I'll draw a proper one with Eagle later on.
The two 100uF would be polarized. The datasheed says 47uF or greater.
@ Wed, 2009-06-10 03:43
Looks very useful
Looks very useful