My Kninja Master always uses a seamless cast on for toe-up socks. it leaves no holes to close up and no CO bumps to worry your toes either. She showed me how to do it, and I could probably do it again if I thought about it real hard, but I'm not sure I can describe it accurately. As I remember, you just wind the yarn in a figure 8 around both needles with the loop that comes over the top of the top needle slanting knitwise ("\") and once you have enough wraps, just pull out one needle and start knitting. Seems like I saw a video for something called "Turkish cast-on" that was similar too -- may have been here actually, but I'm not sure. That one can be done on one or two circs, and I think it was invented using two, but somebody figured out a way to do it on one... or something. It's all kind of hazy now. :zombie: But that should give you something to Google anyway. Seems like Wendy just called the version she uses a "Figure 8 CO".
As far as the CO for the hat goes, I'd just CO 8 sts, join and go, then close up the hole by threading the CO tail or another piece of yarn though the CO sts and pulling it shut like a drawstring bag. (I have a pet name for the technique, but it's a bit ... indelicate.)