I've found you can get on a lot of search engines free. Do it (you must have a webpage, of course).
Do not fall for those that take a small fee and promise to submit you to thousands of search engines, because those simply submit them to the free engines for you. After your sales have gotten large enough to support, get on Google and Yahoo (Yahoo is buying out several of the biggest, so is a good investment.)
Also get a copy to your local newspaper for review, and to local TV if they have a talk show or arts show. Most PBS areas have that.
Get on forums, not necessarily writers' forums, but readers' forums. They can be found by typing "Mystery forums" "Fantasy forums" SciFi forums" etc. in the search box.
Most of the forums will not allow personal advertising, though some have a special thread for that. You CAN, however, mention that you are a writer, and the name of your book, and ask for comment. (A sneaky is to ask a friend to go on the forum and ask you things, which you may answer.)
Some POD publishers will list your book on B&N and so forth, some won't. You have to check that before you contract with them.
Word of mouth is always best, but you have to get the discussion started.
Best of luck!