Surprised at the lack of Chappelli love here. Of those I've read about but never seen, I'd put him at the top. Top-shelf commentator too when he's not rambling about the old days and concentrates on what's actually happening on the field at that moment.
Of those I've seen, Shane Warne. Let's face it, for much of his career, his strengths as a leggie were his accuracy and expertise in the fundamentals (hard-spun leggie, etc.) as he didn't have a huge bag of tricks, moreso variations on a theme. Tactical nous got him a lot of wickets and on that note, as a captain, I've never seen better. Him and Lehmann going head to head as captains would be a treat to watch because when facing each other as players, it was all class.