Mike Nelson did a handful of direct to DVD commentaries over classic B movies for Legend films and then later launched Rifftrax, which were downloadable audio tracks along the lines of what was heard on MST3K - Soon he would be joined by guest, including Kevin Murphy and Bill Corbett - To read reviews, click on a title. A 
indicates an extra special trax. While 
indicates one I could have skipped (Note: I didn't do this for shorts as nearly all would get one). Smilies then would be my recommendations for anyone new who might be wondering what to buy (or avoid). Of course mileage will vary but with so many titles to chose from, it offers a starting point.
and for more Rifftrax reviews, check out gammer's RiffTrax Fan Page