im using a very common switching psu from a laptop or cd player. they are a dime a dozen at recycling shops etc, but i think would be cheap bought brand new too.
they are actually for ac/dc but give em 72vdc and they seem to spit out 12vdc all the same.
there are 2 main types of these, the heavy dongles like on a lot of chargers...with the mains plug directly on the case these have a coil so dont work.
you need the generally slightly longer/flatter/larger and usually lighter type. typically 8v,12v,18v 24v dc output, 90w is the most powerful iv seen, but im sure you can get stronger ones, like this-
http://www.ebay.com.au/itm/AC-100V-240V-to-DC-12V-10A-Monitor-Screen-Power-Supply-Converter-Adapter-/161423634612?pt=AU_Laptop_Accessories&hash=item25959930b4
you can also run say 2x 12v lights in series on a 24v version.
led lights now days have huge output for the watts they use.
i have some 6 watt daytime driving lights-
https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0CFEQtwIwBg&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DpRQA5o2dF_I&ei=zf72VKnMMobZmAXS5oKICA&usg=AFQjCNG9SQVDbhunTvYRm1R_EBvIFs17Kg&sig2=icl0jyYGOhq-RSMdwR65GQ&bvm=bv.87519884,d.dGY
http://www.google.com.au/aclk?sa=L&ai=CyVPdzf72VNmsNsLe8QX1-4KADtHEn5cH-cqj9ZYB4fXS25cCCAQQAiCZqNkeKAVgpcCjgKQByAEHqQIoZYc160WqPqoEJE_QXxew0doMtCRVizi3EU6SYAIFC6fsGkcj_m81O9Zh02i9jIAFkE7ABQWgBiaAB8md8jqIBwGQBwKoB6a-G9gHAeASqY-O6vvKlIhL&sig=AOD64_1Khqm3bpmYZr5k-m5J1Kv9CJbAVw&ctype=5&rct=j&q=&ved=0CCUQww8&adurl=http://rover.ebay.com/rover/1/705-139619-5960-0/2%3Fipn%3Dicep%26icep_id%3D62%26mtid%3D1797%26kwid%3D1%26crlp%3D40593704497_573061%26icep_item_id%3D261756544734%26itemid%3D261756544734%26icep_meta_categ_id%3D131090%26icep_etrs%3DN%26icep_epid%3D-999%26icep_ctlg%3D-999%26icep_cond%3DNew%26targetid%3D75085691617%26rpc%3D0.41%26rpc_upld_id%3D44458%26device%3Dc%26icep_cbt%3Dn%26icep_msku_flag%3Dn%26adtype%3Dpla
stupidly bright for 6watts.
i run 2 super bright led headlights and 2 cob lights and im sure i could run heaps more..