Do you have any road works near you? Fancy a midnight wonder and accidently carry a few bits home?! Cones are good, any sort of sign posts look scary, the weird red and white striped bar things like http://www.westminster.gov.uk/enviro.../roadworks.jpg
(in the background) are good, as are the 3D chunky white and red block things you see in the background of this picture http://www.oxford-chiltern-bus-page....50806%20mc.jpg
At your local hardware store/skip/dump/garden shed you can get the top bits of fencing like http://www.dplumridge.co.uk/themes/D...%20fencing.jpg
if you paint it, then it looks like the fillers you get at shows.
Painted drainpipes make great show jumping poles.
Jumping folded up tarpulin is great for getting horses used to water trays, or of course if you have a shallow tray you can put under a jump then great.
As for cross country - the red 3D blocks pictured above are good, because they are solid and can be stand alone. Sometimes on xc courses you get chunky bright coloured piping, so of course the poles and drainpipes will help for that.
Any branches and logs that fall down in a storm/you jump out hacking/take home with you are good for xc practise. For xc I think its more the idea of getting the horse to jump unusual things and to trust you out hacking which will help. Just make a few solid leaf and bush jumps at home to get used to jumping 3D fences.
Any barrells and things you can get hold off are always good to make jumps out off.
Jump hay bales, and also fences (sj or xc) that have carrots, flowers, cuddly toys, hay bales, picnic clothes, cushions, tyres and cutlery under them! All things I have come across when walking xc courses! They are more rider scarers than anything, but the amount of silly stops at a relatively simple fence because the horse/rider have been too busy looking at the scarer!
Hmmm, sorry it's long! Hope these spark a few ideas - you'd never guess I don't jump!