As a graphic designer, I'm going to assume you already have a decent monitor. In which case a Mac Mini would match nicely, but might not be satisfactorily speedy enough.
That said, a G$ Mini was my first Mac and I happily ran CS on it. Only because budget dictated I had no other option.
If you don't have a monitor at all already... iMac, because speccing a decent new display to complement a Mac Mini is silly talk.
If you want better performance than a Mac Mini but you don't want to deal with iMac's integrated screen (lord knows I have no room for such a machine in my workspace anyway) start thinking MacBook Pro + external.