Hi Simon, welcome to the forum, nice dark skies up there around Albury. I would grab a 4-6mm TMB Planetary eyepiece from eBay ($70 posted from the UK), or grab a 2x barlow for your 10mm plossl (it will double your magnification from 120x to 240x. 240x is a good level of magnification for planets, you can increase this only when seeing conditions are good. As a rule you can use 50X magnification per inch of aperature of your scope, so theoretically you can go up to 400x with an 8" scope but this is seldom possible due to atmospheric disturbance.
An 8mm TMB planetary and a 2x barlow will give you 300x, a nice level of magnification that is not too high as to spoil your view (detail on planets etc.). In order to work out magnification (if you haven't already) simply divide the length of your scope (1200mm) by the focal length of the eyepiece you are interested in. Example below;
1200mm length of scope / 8mm eyepiece = 150x mag
1200mm length of scope / 6mm eyepiece = 200x mag
1200mm length of scope / 30mm eyepiece = 40x mag
You get the idea. As for Nebs you should be looking at larger focal lengths like 15-30mm eyepieces. For nebs and galaxies remember that low magnification (40-80x) with wide field of view (68-80 degrees) are preferable because they take up a large section of the sky and need low mag and a wide field of view to capture the whole neb. For star clusters I like to use 8mm-12mm eyepieces, depending on the cluster and for planets/lunar viewing I like to use anywhere from 3.5mm-8mm eyepieces. remember that the higher power the eyepiece is the less bright the image will be in the eyepiece. So nebs really need low mag to show up.
I would recommend a 4mm, 5mm or 6mm TMB Planetary II eyepiece from eBay for $70 posted to your door (most posters on IIS will recommend this eyepiece at this price) and a 30mm GSO superview from Andrews Communcations (look them up online). They are based in Sydney. The 30mm GSO will cost you about $60 delivered to your door. Alternatively consider something around the 15-17mm range with a wide field of view. The Hyperions are good and can be found second hand in the classfieds sections for around $100. Please note I have included the really bottom end prices for fairly good eyepieces, the GSO and especially the TMB really punch above their weight. For the next level up ($130-$200) I would be looking at Explore Scientific eyepieces ( there is a new Australian dealer for these and people seem to be happy with both the eps and the dealer), Baader Hyperion eyepieces (I sue these and am happy with them, they usually get snapped up quickly as well). Other posters will give you some of the other reasonable brands in this price range.
I would look at getting a second hand laser collimator or even better a cheshire collimator and learning how to use them. There are plenty of videos on You Tube on how to do this. More important than any eyepiece is a realtively correctly collimated scope.
In summary, the TMB and the GSO are good eyepieces delivered to you door for well under $150 but you should keep an eye on the IIS classifieds for really good eyepieces at reasonable second hand prices.
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Yea I know its all cleaned out now , and a new pass word installed ,, yea this is a little off topic , sorry 
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yep bang on Dannat , as usual good advise .
