Where can I submit my press release for online public relations?

Here's a list of press release submission services in Australia, which you may find useful as a starting point.

Australia

PRWire

PRWire offers free distribution services to qualified users. They offer RSS functionality wherein users can have their own RSS feed based on subjects relevant to them. PRWire also offers SEO to their users to ensure high-ranking releases on search sites such as Google.

NewsMaker

This site optimizes your releases to improve search engine results, as well as distribution to social media and journalists. They also offer to increase the buzz your business’ brands in sites such as LinkedIn, Facebook and Twitter. It is a free service which can be upgraded to paid accounts that offers more customization.

Free Press Release

As their name suggests, Free Press Release gives out press releases for free. All users have to do is sign up, create then submit their press release.

Get2Press

Get2Press is an online distribution channel for presentation of press releases to media. They have specialized media lists, which include contacts to more than 28,000 media in Australia, New Zealand, Singapore and 19 other countries in Asia-Pacific via Get2Press. Their media lists include e-mail addresses of key journalists as well as editorial offices of the media.

MediaNet

MediaNet is an AAP business that offers various types of services for businesses. Their Press Release Distribution offers the largest selection of e-mail and fax distribution lists available.

Australia-Newswire

Offers paid distribution through numerous mass media outlets that start from $99 - $999. Australia-Newswire also offers international distribution.

The Media Game

The Media Game is a website wherein journalists and producers can easily view new press releases and download all the files with just one click. A user can also include articles, audio and video files.

Touchpoint Marketing

Touchpoint Marketing consists of experienced and public relations professionals. They offer help on single press releases locally and nationally. The prices range from $800 - $1,200 locally to $1,500 - $2,200 nationally.

Express Press Release

Express Press Release’s network is one of Australia’s largest press release distribution networks online. They also have thousands of clients around the world. Users can avail of their free accounts that distribute press releases in a week. Press releases of aid accounts that range from $29 - $59 are distributed within 24 hours.

Get The Word Out

Get The Word Out delivers your press releases directly to journalists and newsrooms around Australia through the use of e-mail. Their network consists of 2,600 e-mail addresses as well as 67 specialist subject categories that users can comfortably choose from.

In addition, you may want to try Source Bottle.  It's not a press release submission site per se, but you might be able to find PR opportunities by going through the listings.

Hope this helps.