Speaking of þ, it has a role is the oddball "Ye" in "Ye Olde ..." form.
/ðæt/
http://www.macmillandictionary.com/us/dictionary/american/th...In my dialect, the th in with is unvoiced, though it looks like it is voiced in others:
/wɪð/ /wɪθ/
http://www.macmillandictionary.com/us/dictionary/american/wi...It also has further explanation of th is sometimes voiced and sometimes unvoiced depending on context.
One thing to note is that some English speakers pronounce /ð/ and /θ/ as allophones, likely due to their identical orthography. At the beginning and middle of words, it becomes voiced /θɪn/ and /θɪŋ/ (thin and thing) becoming /ðɪn/ and /ðɪŋ/, respectively. At the end of words, it remains unvoiced.
https://en.wikipedia.org/wiki/Voiceless_dental_fricative
th-fronting always catches my attention as well: