There are some herbs that have shown effects, but should be taken under a physician's supervision - gotta be careful - you never know what can happen with herbs or their impurities.
Boswellia - resin from bark - a tree native to India. This 1997 study is pretty impressive if the results are true. Boswellia actually more effective than sulfasalazine which is standard of care.
Effects of Boswellia serrata gum resin in patients with ulcerative colitis.
Department of Medicine, Govt. Medical College, Jammu, J&K, India.
Ulcerative colitis is a chronic inflammatory disease of the colon where leukotrienes are suggested to play an important role for keeping inflammation active. Boswellic acids, the biologically active ingredients of the gum resin of Boswellia serrata (Sallai guggal), have been shown to be specific, nonredox and noncompetitive inhibitors of 5-lipoxygenase, the key enzyme of leukotriene biosynthesis. In patients suffering from ulcerative colitis grade II and III the effect of Boswellia serrata gum resin preparation (350 mg thrice daily for 6 weeks) on stool properties, histolopathology and scan microscopy of rectal biopsies, blood parameters including Hb, serum iron, calcium, phosphorus, proteins, total leukocytes and eosinophils was studied. Patients receiving sulfasalazine (1 g thrice daily) served as controls. All parameters tested improved after treatment with Boswellia serrata gum resin, the results being similar compared to controls: 82% out of treated patients went into remission; in case of sulfasalazine remission rate was 75%.