A couple of tips from experience:
1) Buy/borrow photography magazines. This month I think Practical Photography and DSLR User (maybe others, too) have a page asking readers to send in portfolios etc to be considered for future articles. I tried something similar a few weeks back and 4 days later I was in Paris on an assignment. Most magazines have sections or boxouts telling you how to send in images.
2) Put your pics on Flickr and tag them. You might get a lot of nonsense requests for use of your images, but occasionally a few gems show up. In the past year I've been contacted by two car manufacturers via Flickr (hard to believe, I know, but it's true!)
3) Local papers are pretty easy, shoot enough interesting/relevant local material and you will be published before you know it. If you shoot sports and can write a fewcoherent words that is often a bonus, as away from the major sports (football, rugby, cricket, motorsport etc) which they probably have a pool of photographers for anyway, papers seem to love local interest articles.
4) Enter competitions. A bit obvious, but put the leg work in and it can reward you quite nicely. I'm by no means a great photographer, but I've won loads in the past 2 years through religiously entering most comps in a couple of magazines each month, and as well as published images you often get the benefit of a nice prize as well.