Over at Chiphacker.com, we have a number of list questions. They're all community wiki, and they've been useful. Meta SOFU sites also have lists frequently. I agree that the list has to be manageable (Less than, say, 50 answers expected), and "useful external tools" certainly does not fit that description. However, there are many good questions that would be well served by a community wiki list.
See the meta.SO questions what are community wiki posts and when to mark the community wiki checkbox on a new question
for the official stance on CW posts - The MO community takes a slightly different approach here, which is OK, but we need to decide for this site.
Relevant to this question are the following excerpts (But you should read the whole thing):
Community Wiki posts help enhance the
wiki aspect of the site.
The site is supposed to have a wiki type aspect - Every question does not have a single correct answer!
They make the post easier to edit and
maintain by a wider group of users
CW posts can require maintenance, as a list would.
The FAQ says, "this is a place for
questions that can be answered", but
it doesn't forbid questions which have
more than one answer.
List questions inherently have more than one answer.
Personally, I think that we should allow wiki-type (aka "summary of information") posts, because "wiki" is an element of StackExchange:
Venn diagram w/ blog, wiki, forum, reddit http://sstatic.net/stackoverflow/img/venn-diagram.png
* = StackExchange