I've gotten by with Nestle's semisweet morsels from the grocery store too, and it works fine.
WARNING: Chocoholics may follow you home like you are the Pied Piper when you show up at a party with a chocolate fountain. When I brought mine to my brother's apt for a party and started it up, all the women suddenly surrounded the table and all the guys were standing there with drinks in their hand saying, "Where'd everybody go?!"
I use Gheridelli (sp?) chocolate chips from sams club with veg oil...or 1# hersheys bars, or Symphony bars...
In my area, I have seen chocolate specifically for chocolate fountains. I think it's "runnier" when melted than regular candy melts, and so it flows easier. But you can thin down melted chocolate with shortening, if necessary. When I melt chocolate for a fondue, I blend semi-sweet with milk chocolate (good quality) for a happy medium. Not quite as sweet as milk chocolate, but not as bitter as the semi-sweet. Personally, I like really dark chocolate, but I think I'm in a minority!
I had to restrain myself from buying one of these at Michaels last year where I work. They had the Wilton fountain on clearance for $70 from $129.99, so with the 40% coupon...but I was good...*sigh*
Semisweet is great for fountains, even bittersweet is good when you consider you are usually dipping very sweet fruits or treats into it. I think milk chocolate would be too sweet once you combine it with the dippers. Bittersweet is more chocolatey, but the fountain wouldn't taste sweet enough for most people.
Oh and in addition to the fruit, try Oreos and Nilla wafers too, although they are tough to get them to stay on the dipping forks 
Oh, you were looking at the BIG ones!
I have 5 of the smaller ones that you can get at Sam's, Kohl's, etc. What I tell my brides is:
"I use two of the smaller ones and let me tell you why. First, I don't have $4200 to buy a big 5ft tall fountain. (everyone laugh in agreement!) Second, it takes 10-15 lbs of chocolate just to RUN the big fountain, plus what your guests will be eating, and at the end of the night, that 10-15 lbs of chocolate goes right in the trash .... and you're paying for it. Third, I can get a couple of weddings out of 15 lbs of chocolate, so when my costs are lower, then YOUR price is lower. Fourth, with using two of the smaller ones, instead of one of the larger ones, your guests have more access to the fountains so they can get served faster."
My first ones had 3 levels above the bowl. My latest acquisitions have 4 levels above the bowl, so these hold more and I find I rarely have to refill the fountains during a reception. Sometimes .... but rarely.
I use Dove milk chocolate and it is to die for. I have never had a bad review on it. You have to mix a little veg. oil with it, but it's sooo smoooooth!
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