Piuttosto: a bit of a nightmare to translate thanks to its various meanings. Can be used to express "instead", "quite", or "rather".
Assolutamente: even though saying this makes me feel a bit self-conscious about my accent, I use it a lot. It translates as "absolutely", "really", "completely" or "perfectly", depending on context.
Nel senso che: I wish I knew who I'd picked this up from, especially as I've caught myself using the literal English translation - 'in the sense of'!!