anyone reccomend any casual trousers for mtb/commute use.
have seen ranchsliders on ground effect
website anyone have any or anything similair? (am thinking for summer use)
so dont want anything to heavy!

Just get some under-shorts such at the Polaris Airbase shorts in boxer / Y-front design and use normal trousers (avoiding jeans) combat style pants are comfy and there in fashon at the moment (well in Yorkshire)

Ranchsliders are good to ride in, plenty of room, but they are very very baggy! They are made of a pretty tough material (heavy duty cotton), so are a little hot in summer. I wouldn't recommend them for mtb use - too heavy, but are ok for commutes.

Kona make more mtb-specific pants - I've never tried them but they look quite good. Also worth looking at are very lightweight pertex windstoppers over normal lycras. They are suprisingly comfy and practical. I think Endura make some.

The cheapest combats are, unsuprisingly, from your local army supply shop. Very cheap so good for mucking around in, but they often have a little drawstring at the bottom that might be nasty if it wrapped in your chain.