Spinal Manipulation the evidence?

Plenty of evidence; but generally from poor quality trials. The trouble is that unless a trial is randomised, controlled, and double-blinded, it get's classed as poor quality. There's also minimal funding for research (no drugs, so no money from there, not on NHS, so no money from there, people that do it are interested in doing their jobs, not researchers). You can't really get decent sample sizes, again through the above limitations, and of course, in practice, it's unethical. You also have to ask yourself who a control group would be? remember, you're trying to double blind it, so the control group has to have a sham SMT - which doesn't yet exist; and you certainly can't prevent the provider from knowing whether or not they've done something. Good quality research in this field is basically impossible using good scientific method.

If you're looking at poorer quality research, then there's plenty of evidence both ways, so you can't really draw any conclusions. The only way to really get a useable result is to use a massive sample and compare Chiro/Osteo treatment to GP/hospital treatment, based on subjective measures of outcome; with good follow-up studies; the best example I'm familiar with being Meade et al in '90 & '95 (I think); which led to SMT being recommended in best practice guidelines by the RCGP, NICE, CSAG etc.
You also get the like's of Ernst in Exeter uni who seems to have an axe to grind, and who generally quotes mostly his own work, and who say's it's all a load of rubbish, on the general principal that he can't test for it in a double-blinded, RCT, and there's not the money out there to find new, acceptable research methods to find out; I mention him because he's fairly nedia-savvy, and often gets into the mainstream press; who tend to ignore that his conclusions are often challenged by peer review.

Bear in mind also, that I graduated 4 years ago, so I'm out of date in my knowledge and access to the literature. For a better answer, you'd need to ask someone still at uni, or preferably who teaches there; where they'll be 100% up to date on the latest research, and probably conducting it.

Just come across this as a brief (and biased) overview on the major pieces of research; the article's a few years old now though (2000, though I think this overview was compiled earlier), and there have been 1 or 2 since then; but usually going more into the specifics than these.

1979 The New Zealand Report - a government study originally intended to discredit chiropractic, after two years of worldwide study, published a 3000 page report recommending that chiropractic should be added to the national health program.

1986 OCHAMPUS STUDY U.S. Dept. of Defense, a 50-year study concluded that chiropractic adjustments increased mobility and shortened the duration of treatment

1987 Italian Study - Static Clinics, Milano 70,000 chiropractic patients evaluated showed faster recovery from injury, less time loss from work. Chiropractic is included in Italy's socialized medical package.

1990 Meade Study British Medical Journal Study of 1600 patients showed chiropractic care superior to hospital treatment for low back pain. Recommended inclusion into Britain's socialized medicine.

1992 Dutch Study British Medical Journal Chiropractic superior to physical therapy for long term back and neck pain

1993 The Manga Report, Canada Exhaustive review of current literature established chiropractic care as the most effective, cost effective approach to spinal dysfunction. The study was funded by the Ontario Ministry of Health to find ways to reduce the incidence of work-related injuries and to address cost-effective ways to treat work injuries.

1995 US Agency for Health Care Policy and Research A federal study of 3900 patients, conducted by orthopedic surgeons. Chiropractic recommended ahead of physical therapy or surgery

I can continue...

Naprapathic Manual Therapy or Evidence-Based Care for Back and Neck Pain; A Randomized, Controlled Trial, Eva Skillgate, Eva Vingard, Lars Alfredsson Clinical Journal of Pain, May 2007, 23:431-439
"Naprapathy works better on back and neck trouble than recommended and proven effective advice from doctors, according to a new study from Swedish medical university Karolinska Institutet."

Manual Therapy, Physical Therapy, or Continued Care by a General Practitioner for Patients with Neck Pain. A Randomized, Controlled Trial, Jan Lucas Hoving, PT, PhD; et. all.
"Conclusion: In daily practice, manual therapy is a favorable treatment option for patients with neck pain compared with physical therapy or continued care by a general practitioner."

Manual Therapy Best Alternative Treatment for Neck Pain Relief
Ann Intern Med. 2002;136(10):713-722, 758-759
"After completion of treatment, success rates were 68.3% for manual therapy, 50.8% for physical therapy, and 35.9% for continued care."

Korthals-de Bos IB, Hoving JL, van Tulder MW, Rutten-van Molken MP, Ader HJ, de Vet HC, Koes BW, Vondeling H, Bouter LM. Cost effectiveness of physiotherapy, manual therapy, and general practitioner care for neck pain: economic evaluation alongside a randomised controlled trial. BMJ. 2003 Apr 26; 326(7395):911.
"manual therapy is faster and less expensive in relieving neck pain than more traditional types of therapy."