I have a popcorn maker and I find plain pop corn (with NO butter!) very filling and low calorie. I season it with paprika for a nice flavour - this also means I'm not adding salt.

depends on what you want, sweet or savoury etc... any food can be slimming eaten in moderation, i dont believe any food should be eliminated, if you want a biscuit eat a biscuit, but stop at one...
generally biscuit and sweet wise things like ginger nuts, party rings, rich teas, fig rolls and a good digestive alternative is hovis crackers, theyre just like digestives but only 38 calories, theyre in a red packet. chocolate wise, again any chocolate can be a healthy snack if you only have alittle bit but things like kit kats, fige bars, freddo bars etc.... are all around the 100 calories mark. svaoury wise, if you want extra healthy try crudites like celery, cucumber, carrot batons, with hot salsa or crisps like skips, quavers french fries and the weight watchers ones are quite nice, theyre all around 100 calories. to be honest most crisps have been made healthier because of all the hoohaaa surrounding obesity so not many packets have more than 150 calories, except things like mccoys... although be warned multipack crisps are smaller so lower in calorie than the single bags so go for multipacks