I am a Canadian planning to visit Europe with my family later this year for about 6 months. I am aware of the Schengen 90-180 rule that says I may enter the Schengen zone as many times as I like within a 180 day period as long as I don't exceed 90 days in total. So, to make the most of our 6 months we are planning to spend only 90 days in the Schengen Zone and the other 90 days or more outside of it. Does anyone have any up to date information on which countries 'stop the clock' and are not included in the Schengen 90 day limit? I am considering UK, Ireland, Croatia, and Montenegro. Are these countries considered outside of Schengen for 90 day purposes? Are there others close by? Is this info posted on any official euro-government type sites? Thanks in advance.

Yes, UK, Ireland, Croatia, and Montenegro are outside of Schengen and will not count toward 90 days. Serbia, Bosnia, Romania, Bulgaria, Albania, Macedonia, Ukraine, and Turkey are also outside of Schengen. Morocco is not Europe, but only a short hop from Spain. Similarly Tunisia is close to Italy. Syria, Jordan, Israel, and Egypt close to Greece and Cyprus. From my experience the 90 day limit is not strictly enforced, as long as you don't exceed 90 days in a single visit in the Schengen area.
The four states you mention are not in Schengen, also Turkey,Cyprus and Serbia aren't, as well as Eastern European states like Russia or Belarus.
If you spend 90 days outside of Schengen, you get another 90 days inside. If you have time enough, there's more than enough to see in the UK and Ireland alone.

Here you heve a list of the "Schengen Countries" - all the others are not.
http://www.axa-schengen.com/en/schengen-countries

However, a recent post from a clued-up traveller who did what you plan to do reported problems in Hungary. Although Hungary is not part of the Scengen zone and so time spent there should not have counted against the 90-day limit, Immigration officials thought that it did since Hungary is part of the EU. The poster was refused entry to Hungary and even had a "denied admission" stamp in her passport.
Hungary joined Schengen in 2007. I suppose the traveller had checked a list of states before this date.

Although Hungary is not part of the Scengen zone and so time spent there should not have counted against the 90-day limit, Immigration officials thought that it did since Hungary is part of the EU.
You've slightly misremembered what the problem was. The issue was not about whether time in Hungary counted towards the 90 days - everyone agrees that it does. The point in dispute was whether countries in the EU but not in Schengen should count - specifically UK/Ireland/Romania/Bulgaria in his case. The traveller had spent time in these countries in the belief that it wouldn't count towards his 90 days. The Hungarian border guards claimed that it did count because they are EU countries. That goes against the way most people on this forum think the rules should work, but that wasn't much consolation to that particular traveller.
I suppose the traveller had checked a list of states before this date.
No, the traveller was very well-informed, knew exactly which states are currently in Schengen, and exactly followed the advice often given in this forum.
It's worth noting that this is, so far, the only case of this type we've seen reported on this forum. Difficult to say if it is specific to entering via Hungary or not.
There will certainly be no issues with Croatia, Montenegro, Bosnia, Serbia, Macedonia, or Albania - a very interesting group of adjoining countries in the Western Balkans that are well worth spending time exploring, as these countries are not in either EU or Schengen. Similarly for Turkey, Russia, Ukraine and Belarus.

This is the thread mentioned above:
http://www.lonelyplanet.com/thorntree/thread.jspa?threadID=1902639