Jewelry is always an appropriate gift. The bigger and more glamorous the better. Don't waste your time on cute little trinkets, go for the gemstones every time. Earrings, watches and necklaces head the list. Make sure they are dazzling... Aries loves a bit of flash.
Tickets to a sporting event they enjoy will make them happy. Likewise, gear for a sport they participate in is a good choice, as are clothing or hats emblazoned with their favorite teams.
Aries likes to stay active and learn new things. Find out what has been intriguing them lately and get them a how-to book on the subject, preferably with some materials to start their newest project. For example, if your Aries has been longing to knit, buy them a great instructional book with lots of diagrams and pictures as well as a pair of needles and some nice yarn.