In academic Computer Science, there are basically three publication venues that "count": peer-reviewed conferences, peer-reviewed journals, and peer-reviewed workshops/symposia. There are of course many other perfectly credible ways to publish one's work (e.g., technical reports, books), but these are the top three.
Unlike in most scientific fields, including our closest cousins Engineering and Mathematics, journals are not the de facto place to publish papers. I can't speak for all subfields of CS, but basically everyone I know only publishes in journals because they feel they have to (e.g., multi-disciplinary tenure and promotion committees that expect journal publications, research rankings organizations that still don't seem to 'get' conferences, etc.). Some subfields this is not the case, such as in interdisciplinary fields like Bioinformatics and CS Education, but for most major areas of CS, conferences are where the action is.
For these fields, the top conferences have extremely low acceptance rates, many less than 17%. The program committees are comprised of the top scholars in the field. And in some fields, anyone who is anyone attends these conferences, so managing to get a paper accepted is a pretty big deal that gets a researcher much visibility.
Some journals have similarly rigorous standards of review and are known for their quality, for example the IEEE Transactions and ACM Transactions family of journals are highly regarded. There are occasionally other journals that are good, but the vast majority are either decidedly mediocre or utter rubbish. We don't really have any comparable C/N/S type journals.
Workshops and symposia generally have a much higher acceptance rate than conferences and journals, but they are still peer-reviewed and are often archival (e.g., ACM Digital Library, IEEE Xplore). They have quite a few advantages. First, they are usually co-located with a conference, which means you can often go to both on your University's dime. Second, they present a fantastic opportunity to float half-baked ideas and get one-on-one feedback from your peers. And third, oftentimes workshops are the only place you can meet other scientists interested in the same area of specialized research as you, which nearly always leads to good things.
But the most useful thing about conferences and workshops over journals is that you have the opportunity to tell potentially hundreds of people about your work. These are all people who learn your name and face and start to match it to a research area. This is invaluable, because it leads to professional relationships that will see you through your career - jobs, funding, tenure/promotion letters, etc.
Journals don't really get your name and face out there as well, unless some news outlet picks up on your article. People do read journals, but I suspect most readers associate papers more strongly with an institution than a name, particularly if it's a new name on the research scene.
So I think it's nice to have a diverse portfolio when it comes to publishing. It's good to have a mixture of papers in the top conferences with low acceptance rates, in journals that are well-respected, and in workshops that are useful to the researcher.