We will take care to advertise your book in the 100 or so largest search engines. If you like, you can make sure that every single one of them knows where to find you. However, if you are selective and discreet, there is nothing wrong with advertising that you have a book for sale in the newsgroups devoted to your subject or genre. You can engage in an email advertising campaign. There are services that will send your message to 100,000 recipients for a few hundred dollars.
Email advertising is inexpensive and an excellent way to get the word out.
You can take out a small advertisement in the backs of magazines. If your book is of interest to astronomers, you can use several astronomy magazines. If you have written a mystery, then there is Ellery Queen's Mystery Magazine . Third Millennium Publishing is not a publisher of authors so much as it is a cooperative of authors. Each writer who participates is selling his or her book directly to the public and collecting the revenue.