Tramadol can be a very enjoyable and worthwhile investment (if you like drugs that is). It is noticeably stronger than codeine and about the same strength as hydrocodone and oxycodone. It is generally used for medicinal purposes as a relief of severre pain.
From experience I would say the following are good dosage estimates.
Light High - 50 - 100mg
Medium Intensity high -100 - 250mg
Good all day high -250 - 350mg
Note: doses exceeding 350mg don't seem to intensify the experience noticably and doses exceeding 500mg often produce undesired effects ie. nausea, vomiting etc.