Sheila, I think I said in your other thread (was it yours?), I used Lulu for the last project, 'cause it was just a private, family thing, but I shall almost certainly use Diggory for my novel.
I have dealt with Trafford and Authorhouse through my job (I source and buy special interest books for a library service). Their products are good enough, but they charge a lot to the author and that's not something I can afford when I probably won't make any money back out of the deal.
I'm afraid there's always been this argument over the worth of self-published material - some writers swear by it, others abhor it for all the reasons cookiee has said. Cookiee is not entirely wrong in what he/she says, in that self-published material is traditionally looked upon as no more than vanity publishing for unpublishable authors, but there is some decent work coming through, and there are a few suppliers, publishers and agents who will keep a look out for promising material in that sector - although you shouldn't bank on that.
Just be realistic, do your homework and keep your eyes open all the way, and you shouldn't get ripped off. In any event, be very wary of a company called Publish America. Haven't room to say much here, but run a search in Google and you'll see what I mean.