I think for all websites it would be a MUST to ensure the RSS icon is displayed in the address bar!
But there are tons of pages, who don't care and even hide the RSS icon somewhere on the site.
What do you offer your clients, where to place the RSS icon?
Is there a so called optimal placement? Is there any study on this topic?
Unless you have multiple feeds, I would place it in the same list as your social profile icons (not to be confused with "share this page on social networks" links).
As for the best location of this list, it was discussed in the question Social share buttons best position (on top of the page seems to be the most popular).
Also, you may want to read the article "RSS is Being Ignored, and You Should Be Very Worried" about the recent changes of RSS support in web browsers.
The optimal placement depends on what the RSS feed contains. For example, some sites provide multiple RSS feeds from the same core data set.
I worked on a system that collected reporting for an organization from around the world. These reports were organized based on origin, topic, and date (think geo-location and tags). The organization's analysts and the analysts from cooperating organizations only cared about slices of information. Once the user narrowed their scope of what they wanted, they could get a dedicated RSS feed for that scope.
In this case, we had a link for the custom RSS feed in the right panel above the tag cloud for the feed. The list of items was in the left panel.
This particular system also supported comments, and for particular hot topics it was useful for the analysts to have an RSS feed for that one article. The only had to look in the same location for the RSS feed when they were looking at an article.
Does this mean that everyone should have a 2:1 split and have RSS links at the top of the right panel? Hardly. It takes time to understand your audience. It made the most sense for this project. It seems to make a lot of sense for blogs. However, you may want to emphasize the RSS feed more by having the link at the top and bottom of the lists. Or you may reverse the split we had. You just have to fit it into your design and remain consistent with it's placement.
Following the assumptions in this question: https://cogsci.stackexchange.com/questions/2056/any-research-on-right-hand-left-hand-based-preferences-when-interacting-with-an , I'd recommend generally sticking to the top-right corner of the page.
Note: on this very SE page, the rss link is on the lower-right corner of the page. This makes sense in this isolated case, because you are likely to want to subscribe to the feed once you've posted an answer and the lower-left corner is within your visible area upon submitting your answer.
But come to think about readers who do not contribute new answers but would rather only want to reader them, then having it duplicated on the top-right corner would still remain valid.
It probably makes more sense to include all the site-wide feed options in the address bar. If they are included in the page markup most browsers will allow you to select which site feed you subscribe to when you click the address bar.
Then, if you are including more granular feeds in the page/article itself they should be contextually placed in a clear relationship to what they are related to. You can also consider appropriate attributes or description text with them to clarify.
I think that an RSS icon should be made to appear on the address bar and somewhere in the page. The address bar is where RSS junkies (and likely power users) expect it to be. You can make the browser display the RSS icon with some HTML code:
<link rel="alternate" type="application/rss+xml" title="..." href="..." />"
Where to place the icon on the page depends entirely on the contents, as @Berin pointed out, but:
Having it in the footer is always a safe bet. This doesn't prevent you from putting it somewhere else as well.
I strongly recommend that you do not use the RSS icon exclusively. Add the word "RSS" as well, for two reasons: a) accessibility, and b) when a page is very busy, I often search to look for the RSS link within the page; it's frustrating search fails and have to scan visually.
Depending on content, beware that Safari 5.0 will now display its Reader icon instead of your RSS icon, if the contents of the page can be displayed by its Reader feature, e.g.:
In other words, make sure that the RSS icon in the address bar is not the only place that it shows up.
The optimal place for any icon is the place on the page where:
Typically this is somewhere close to the title, or a very prominent control group; but your case may well be the exception—it all depends on context.
Let's take some examples for RSS:
