I wasn't that impressed by the CoolMedics stuff either... problem is, if you live in a vaguely humid climate, the vests don't work like they're supposed to. If you're somewhere dry, I gather they are excellent. If you stay cooler simply by virtue of being slightly wet, they can be helpful in that regard. I don't think it was a total wash having one, but I was less than enthused about its cooling properties. Mostly it just got me very wet.
As far as other things to try, I also got a phase change vest last year, but never wore it because it is HUUUUUUUUUGE. It's possible they've come out with something less bulky since then, so those are worth looking into.
I've also tried a small gel icepack in my helmet (great at the beginning, then melted and heated up to boiling point later in the ride, thus exacerbating the situation!) I also tried the CoolMedics hat thing and thought it was pointless.
Gold Bond powder is helpful for some reason. Slight cooling effect, which for me seems to last awhile.
Other than that, all the CoolMax stuff you can possibly find.
I have a Hyperkewl (similar to CoolMedics) vest and find that it keeps me cool most of the way through a strenuous 45-minute ride if I stick it in the freezer for a while and put it on just before I mount up. I'm pretty heat-intolerant and the vest is the only thing that gets me to ride when temps are over 85. I find it also helps with barn work as long as I stick it in the freezer every hour or so, so I tend to work on stuff in the heat for about an hour, then find something in the air-conditioned lounge to do for half an hour while it chills back down.
I'm a big fan of cool medics products and have the vest, neck cooler and a poll cap for my horse. However, I'm in Northern California and we don't often have humidity so it could be that humidity plays a factor in how well it works.