Frame a photograph of the two of you and add a little love message.
Jewelry is a lovely six month gift as it is something that will be close by them every day, you could be an old fashioned romantic and give a locket with the photo of the two of you in.
Music is also very personal. In the 'olden days' you could put together a tape full of songs that you know that they would love. If they still have a tape player then that would be a fun retro gift. If not then how about borrowing their mp3 player and putting together a playlist that means something to the both of you.
Days out and trips are a great way to celebrate your first six months, you could go back to where you first met, your favorite restaurant or go somewhere you both have wanted to go to for ages. An anniversary is a great excuse to go out and celebrate in style!
There is no specific gift on anniversary gift lists for your six month anniversary but instead you could look at the number six for your theme.
Six love notes
A treasure hunt with six clues and a romantic date at the end