By country, off the top of my head. Obviously more Indians since I primarily watch Indian cricket. Only current commentators are noted.
India
Ravi Shastri
Not overly biased, has poise, speaks really good English and doesn't make silly mistakes. Has several anecdotes to share and gets along with most other commentators. ESPN built him up as a "color" commentator as well, by adding the Shaz-and-Waz show during India's tour of Australia in 2003.
Sunil Gavaskar
One of the most knowledgeable blokes around in the commentary scene from an Indian perspective. Is quite biased towards the Indian team and of late has been getting annoyed easily when things don't go his way (early onset of senility, perhaps?). This was in evidence during the wrap-up shows during the Sydney 2008 Test match.
Harsha Bhogle
For someone who has never played cricket professionally, he has a ton of knowledge. Primarily a host, he has swung his career into commentary. Provides good insight as to how a regular viewer might perceive cricket, having not played it. Can sound geeky after a while.
Australia
Ian Chappell
I'm 50-50 on Chappell. He has a lot of knowledge and can keep me interested for ages, but he can also annoy the hell out of me when he's speaking. His "holier-than-thou" attitude is somewhat frustrating, but at the same time he talks straight without sugaring his opinion, something that is quite respectable.
Michael Slater
One of the more biased Aussie commentators going around and he got into my list over Dean Jones because... well because Dean Jones is quite controversial. Has a strong bias towards the Australian team that comes from being closest to the latest generation of players, but is exciting to listen to nonetheless.
England
Mark Nicholas
Very, very smooth talker. Doesn't give the impression of giving commentary as much as giving the impression of talking about a game with a couple of buddies, which makes it very easy to listen to.
David Lloyd
Love his accent! Seriously, though, he's one of the few commentators on the Sky team that I can stand. He's a little biased against England (irony?) but has plenty of interesting thoughts and usually ends up playing mediators between the other commentators in the box.
Pakistan
Wasim Akram
One of the finest Pakistani commentators out there and one of the finest gentlemen to have played the game, as well. Unlike his compatriots, he is quite unbiased, in my opinion. His command of English isn't perfect, which shows that you don't have to speak the Queen's English to be a good commentator.
West Indies
Michael Holding
Haven't heard him commentate recently, but I remember him from the last few years as the one guy who could make any event in a cricket match sound ridiculously cool. Must be something to do with that Carribbean accent.
Ian Bishop
Again, haven't heard him recently, but he did a lot of India's matches at one point. Pretty even commentator and easy to listen to, as well.