Most of mine were tribal, they're an easy and cheap way of building a competative deck. My first and probably still one of the best is a solo white cleric deck which pretty quickly can be like trying to make a dent in water.
At one point I wanted a solo red deck that wasn't simply direct damage or land destruction so I built one that started with Silth Firewalkers and all the 'either or' cards like browbeat, skullscorch etc plus the artifact that lets you double up sorceries, sure its a bit cheesy and some people take being beaten by it better than others but if I have to sit through sliver, elf and artifact decks I don't feel too guilty about pulling this one out every now and again.
I was just starting to get the wizard deck happening the last time I was playing. It all started because I liked willbenders so I added fatespinners, Meloku and some others. I was starting to win more than I lost with it but it still needs some work.
I think one hint that still holds true is that your deck should be 60 cards with very, very few exceptions. If your main strategy doesnt involve digging through the deck alot (or stripping both players of cards and winning by having more) then anything more than 60 cards is just reducing the chances of getting your best combination, each deck should have clear strategy/s, focus on that and cut out what you have to.
White and blue are still my favourite colours, I occasionaly use red or green but Im yet to make a black deck that was any good even though its probably the toughest colour solo. So what about everyone else favourite colours or card types?