Lydia, I can't really specify any items, as I haven't seen any of this years stuff yet, but can offer a few ideas.
The usual top-of-the-tree things are stars, fairies, angels and those bauble type things with a pointy top.
Why not opt for something unusual, like a crystal beaded snowflake, you could probably make one yourself from wire and beads. Look in Hobbycraft for beads and books on beadcraft, they may even have a small 'how to' card telling you what you need for craft items.
Or a large fancy bow with jewel detail, imagine a velvet bow with a diamante brooch on it for a glamorous vintage theme.
Or for young DC, a snowman, santa, robin or pixie.
I find that garden centres have good selections of Christmas decs, sometimes better value for the quality than high st stores. Also check out internet shops, and interior design catalogues festive ranges for inspiration.