While watching the Danish show Borgen last night I noticed that Kasper, when talking about ordering a smoothie, first said [smu:di] and then later said [smu:ði]. The first form in particular but also the variation pleased me, so I asked Anna Jespersen about it and look at this bonanza she came up with! (What follows is a paraphrase of what she sent me.)
Smoothie is a newly borrowed word, and I think it's the only one we have encountered with a non-initial [ð]. Consequently, there's a lot of variation. [ð] and [d] would be the most common variants but there are lots of other options. Check out these two ads from McDonald's:
i. In the attached print ad, the line below the smoothies reads "Try our new, refreshing smoothies (no matter how you pronounce them)".