Thanks again for the replies, very useful! From what you have said it seems 6x6 or 6x7 seem to be the easiest to use or most versatile.
wy2l: I do think I would prefer to get an SLR, mainly because if I bought a TLR then decided I still wanted to try SLRs then I wouldn't be able to afford it, so thanks for the help. I've been looking at the Bronica SQ series and I really like the look of them, but unfortunately unless I get lucky I don't think I will be able to afford one. And not to worry, I have a great Manfrotto 055CF tripod and 055 ballhead that I use with my 60D.
Thanks jspillane, very useful information! But I'm still not entirely sure, would 6x4.5 be suitable? Or should I look to get something like 6x6?