So, I've been using spotify for some time now, but I found out recently that it is quite easy to publish your own songs to it as well, and it doesn't cost very much at all.
Spotify works with a number of indie agregators. These sites do the paperwork needed to post your songs to spotify, itunes and a host of other download sites. They also deal with the royalties, which come back to you.
Here is spotify's list of sites - there's quite a few to choose from, and they all have varying terms and conditions, coverage and pricing models so pick one that suits you.
http://www.spotify.com/en/work-with-us/labels-and-artists/aggregators/
For an example though, here is my take on http://www.dittomusic.com, one of these aggregators.
Ditto Music has various packages depending on how many online sites you want your music to go to. All of the packages are subject to a £2 per month charge per release. A release is the equivalent of a single or album, so it is more cost effective to put up an album than a single.
Their coverage packages then start at the most basic, which is spotify only and has no upfront fee - to their premium package, which is £50 up front but puts you on over 700 stores (albeit, quite a few of these are regional variations of the same brand - itunes in europe, itunes in america for example)
They also have add on options to make your record chart registered, and they will do the legal paper work for you to set your own record label up for 25 quid (they also tell you how you can do it yourself and exactly what they are charging you for - the legwork, essentially, it's not a hard process when it's written down for you)
Is it worth putting your music on spotify? Well I'm thinking of doing it more for personal satisfaction than the intent of making money. But first, gotta finish that album!