UPDATE (8 Aug 2011): If you have previously cloned my Yahoo! Pipe you might want to update your feed URL to http://twitter.com/statuses/user_timeline/64445277.rss?count=200 as WealthEsteem migrated the ASX announcements feed to the @mktbot account. Alternatively just re-clone my pipe.
A few years ago I created an RSS announcements feed which could be customised to specific tickers. It was picked up by a few blogs and when I had to shut it down in early 2007 due to ASX complaints I received quite a few emails asking about alternatives.
I have no want to host such a feed again as I have no interest in battling the corporate bureaucracy of the ASX.
Enter Yahoo! Pipes. Pipes provides a simple, semi-programmatic interface for building RSS feeds (amongst other things). You don't need to write any code but having some basic technical understanding helps.
I have built an example pipe that uses the WealthEsteem Twitter feed, filters it down to particular tickers, and re-writes the RSS link so that you go straight to the ASX PDF (otherwise the Twitter RSS feed would link you back to Twitter).
You can use this feed by simply entering your desired tickers as shown below:
Alternatively you can clone the Pipe and modify it further for your own needs.
Limitations: The Twitter RSS feed returns a maximum of 200 items. Since the feed includes announcements from ALL ASX listed companies you may miss some announcements depending on how frequently you refresh the feed. I don't know how much of an issue this will be in practice - historically the maximum number of announcements I've ever seen in a 24 hour period is 1958. Typical days are 200-600 announcements. So if you refresh every 30 minutes or so you should be right.