I know Australia uses the ranked ballot.
House of representatives is preferential ("instant run off")
Senate is preferential proportional representation.
they key is, whatever you choose, the two houses should have different systems so diversity ensues (it makes it more likely the government thats formed in the reps has a hostile senate it has to negotiate with - i.e its no rubber stamp).
i.e the Australian Senate is far more likely to get minor parties/independents than the house - proportional allows for more diversity as you need less of the vote to get a quote for a seat (Australian senate: 6 states x 12 senators per state, 2 mainland territories with 2 senators per territory - only half the senate is up for re-election at each federal election (senators have 6 year terms). With straight preferential the horse trading is in preference swaps/deals: general flow is the Greens preferences 80% flow to the ALP (and more or less the same the other way) - and they rarely can get enough of the primary vote to win themselves, you'll hear the ALP "winning a seat on greens preferences".
You'll hear alot about the 2 Party Preferred vote - which is basically the % of the vote the last two candidates get (preferential: win of the seat means that you have 50% Plus One (the absolute majority) of the vote in the electorate).
Senate ballot papers look cumbersome but you have a choice: vote "above the line" or "below the line" - voting above (which lists parties) you only number one box to make your vote valid, and you are in effect voting with the party's (who you selected) preferences for other parties. If you vote below the line, you must number each box for the ballot to be valid. House of reps are simple and generally have smaller amounts of candidates and you must number every box in preference order. All political party's hand out "how to vote" cards before you go into the polling booth (for reps and senate), which explicitly state their party's preference flows - you can ignore them or follow them (far more likely getting people to do their own preferences in Reps than Senate given the Senate ballot generally has 2-3x more candidates than reps). Liberal and National party (in an almost permanent coalition) mainly get their preferences from conservative / rural indies.
All states generally use the same type of system for their lower house (QLD only has one house), the ACT has a whacky/fucked-up/Eurotrash system that barely anyone understands (territories only have a lower house as in effect the Federal Senate is their upper house).
edit: The Wiki page explains the voting systems very well (in a lot of detail): http://en.wikipedia.org/wiki/Electoral_system_of_Australia