Here's a comparison chart of Hulu, HuluPlus, and Netflix. Some notable tidbits:
-- Free Hulu doesn't have too much in the way of full seasons, but they're not without their gems. Especially older shows like Highlander and Doogie Howser. Though, putting Doogie Howser behind a paywall would be as cruel as requiring a subscription to Xbox Live just to play that Netflix Streaming you already pay for on your TV.
-- HuluPlus does offer an impressive library of back episodes, but it does get bested more than once by Netflix' library. Though, apparently Netflix' interest in maintaining an impressive television show library starts to taper off after shows that start with B, with a serious prejudice to Cs.
-- While I'm fairly certain it did not affect the data presented here, while collecting data, some shows were added or removed from the listing on the promo page for HuluPlus. It is entirely possible that the data here may be incorrect by time I submit this article.
Yes, some shows are on Netflix, and also Amazon and iTunes (but you'll have to pay for each episode or season via Amazon and iTunes). And you'll have to wait at least until the next season for them to become available.