The easiest one that I know is DoGA CGA. It is designed as a series of lessons (L1, L2, L3.) It is not a 3D modeller per se, but more like a 3D studio full of parts that you assemble to make your models. It has .X export so you can use the models with Dark Basic.
http://www.doga.co.jp/english
Each lession is free to download and use. You can register L2 and/or L3 if you want to make AVI movies.
L1 and L2 have English help files and I made a translation of the L3 Parts Assembler help file when you get to that point.
Due to its parts bin metaphor, DoGA CGA excels at mechanical things. Jets, space ships, power armor, giant robots, etc. It is a good stepping stone to other programs. Once you master DoGA, moving on to 'real' 3D modellers is a lot easier.
--
TAZ, unofficial (as in unpaid) English speaking DoGA guru