Is a letter of recommendation from a former boss extremely important to a job application?

I'm applying for jobs, but my former employer is really a slacker when it comes to writing a letter of recommendation. Even when I worked for him, it was frustrating because he wasn't on the job site so the main communication was by phone and email, and he would never respond or pick up his phone etc. It was so hard to get a hold of him and he never followed through with what he said he was going to do. He's very flaky and isn't that responsible, and really I'm glad that I don't work for him anymore. But since the company downsized and I lost my job as the newest employee (last hired first fired type of thing), I've been having trouble reaching him again to get a letter of recommendation. He told me that he would write me one, but since I've emailed him to ask, he sent me an email saying he would work on it over the weekend, and that was 2 weeks ago! I emailed him asking if he was finished with the letter a week ago, and no response. I'm starting to get really frustrated because I need to list that job on my resume for experience but after being laid off it looks really bad if I don't have a letter of recommendation from my former boss, doesn't it? I have a letter from a coworker, but my former boss is just such a flake! Is it really all important for a letter of recommendation to be from a boss and any advice about how to get this from him???? Thanks!