- WordReference.com: Like with Spanish, WordReference.com comes in first on my list of Portuguese-English dictionaries. However, its Portuguese dictionary is not as good as its Spanish dictionary primarily because there seems to be a big gap between the two in terms of word count. For Portuguese too there are forums available in which you can get answers to specific questions, but the forums are much less developed than in Spanish. You should still be able to post any question about how to say something in Portuguese that you might care to, but the body of already-answered questions is much smaller than in Spanish. What's more, the Portuguese dictionary seems to be very Portugal-centric, so for those of us that consider Brazil our home in the Portuguese-speaking world, that's a big minus.
- Reverso: Reverso's another solid choice for a dictionary, but Wordreference.com seems to have it beat in terms of breadth, and certainly in terms of the forums. The one thing I do like about Reverso is that, when there are multiple Portuguese definitions of the English term, it gives you a parenthetical that helps you figure out which is the appropriate term (take the entry for "stock", for instance). It's sometimes clearer than Wordreference.com because of this.
- LookWAYup: Look way up doesn't have the word coverage that the above two do, and its definitions are pretty basic, but on occasion I've found it has filled a blank the other two couldn't.
All in all, the currently available dictionaries for Portuguese aren't quite as good as those for Japanese, Chinese, or Spanish. The most fundamental problem is their limited word coverage, but Portuguese dictionaries also don't have as many example sentences or options to hear the pronunciation of the words online. However, with Brazil on its way up as one of the BRIC countries, I'm hopeful that this situation will improve over time.
As always, let's hear what you've got to say in the comments below—especially if you can point me to an even better dictionary that I missed!