If you're serious, get either poker tracker (with PokerAceHUD) or poker office. Basically they track everything you do, great for identifying leaks. PT costs $55 (plus $25 for PAHUD) but PO can be got for free (easiest through Party if you aren't a US player).

Sharkscope is reasonable, but don't take it too seriously, some people play alot on different sites which aren't covered.

Poker x factor is supposed to be pretty damn good, but it's pricey, especially if you're just starting the game. Same with Cardrunners which is ideal for learning cash games but, again, is a bit pricey to start with. It depends on how serious you are, if you really wanna make a go of poker then sign up to one of those sites and see how you get on.

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For Free Money, Poker Gifts and Rakeback I recommend PokerSourceOnline.

I have to recommend Cardrunners for superb poker coaching. It was honestly the single biggest improvement in my game signing up there! Sign-up fee might seem steep, but it pays itself back within weeks.