Welcome karnash,
Unless you're really after a fresh look for your Liberty I would suggest that you place your focus ( and money for that matter ) on getting the best new tyres you can afford on the existing factory wheels.
The reason why I've made this suggestion is twofold,
Firstly there's not a lot of wheels available in the aftermarket range that will fit the Liberty because of it's higher than normal +55 offset. If you don't get a wheel that is close to this offset ( =/> +45 ) you'll not only have issues such as incorrect tracking, but in some cases have a wheel that won't clear your brake calipers - OUCH ! If you are after something different, I have a set of 4 near new 17 inch GMAX Defiant wheels still available for sale ->
http://forum.liberty.asn.au/viewtopic.php?t=4112
Secondly, if you decide on getting new aftermarket wheels that are larger in diameter than the factory ones you have now, say a set of 18 inch rims. The price of the rims and moreso, the price of tyres goes up considerable, not to mention the choice of tyre brands/models are even more limited when you go up to 18 inch tyres than the current 17 inch factory wheels. Also, by going up in wheel diameter size, the profile/ratio of the tyre will need to come down and the resultant ride will be firmer and some maybe considered to be "harsher".
The guys previous to me have already covered the importance of maintaining the correct ride height of the tyre ( overall rolling diameter of the tyre ) and as you can see, it's not as simple as slapping on a tyre of the size you prefer.
I recently purchased a set of Pirelli Dragons in the 215/45/17 for $205 each which I'm really happy with. I have also previously used the Yokohama S drives @ $255 each and the Goodyear F1 @ $325 each.
I have also previously used Michelin Pilot Preceda tyres which have fantastic grip, but their pricing have gone through the roof in the last year or so which makes them harder to justify.
Anyways, hope this information is helpful to you in making a decision.
Cheers,
Lok