Sonnani also modifies an adjective. "Watashi wa sonnani kawaikuarimasen." I'm not that cute.

there are two different meanings for そんな (sonna) 1: that kind of; such a ex:　そんな情けない息子は認めない！(sonna nasakenai musuko ha mitomenai!) "I don't accept such an/that kind of abject son!" 2: oh no!; what a pity! ex: 　“父さんに亡くなられましたんですって？そんな。。。”(Tousan ni naku nararemashitan desutte? Sonna!) I was told/ So you are telling me that your father has died. What a pity!/ Oh no!/ How could it happen? そんなに (sonna ni) means "so much", "as much as you say" ex: わたしはそんなにつよくありません。　(Watashi ha sonna ni tsuyokuarimasen.) (I'm not that strong.) There are also Konna and Konna ni. Both mean the same as sonna and sonna ni, but with the difference of space of "here" or "near me" that kono expresses (that`s where konna and konna ni comes from) and "there" or "near you" that sono expresses (that's where sonna sonna ni comes from) hope I helped out (sorry for the last part seems to be a lot confussing, feel free to ask me any doubts about my answer)

You can find the answer at http://www.italki.com/answers/question/90271.htm . See the best answer.

1. sonna Modifies a noun. This kind of thing. 2. sonna ni Modifies a verb. I did it this (kind of) way.