Among the more exciting items would be to get your own weather station, and there are many choices from several different brands. You can spend anywhere from less than $100 to thousands, with most home-use complete stations running in the $300-$500 range.
The biggest brands are Davis, Oregon Scientific and LaCrosse. This article I wrote a few years' back can give you some guides what to look for in a weather station. You can even get software to put your weather data online, depending on the station you purchase. Some of the most popular are WeatherLink, Virtual Weather Station, or WeatherView32.
No matter what you decide, shop around online as you can find a wide variety of prices.
For practical and pretty, I have a Galileo Therometer & Barometer that has floating glass balls inside a liquid that tell you the temperature inside. Some models have a liquid barometer attached as well. It makes a nice addition to a bedroom or office.
Books are always great to spark interest and easy to slip under the tree. There is, of course, the book Steve Pool and I co-authored in 2005 Somewhere I Was Right which is a fun look at weather around the Northwest. It's a bit hard to find online these days but it's now available in most Seattle-area Tully's Coffee locations with $10 of each book sale going to Hopelink Charity.
I'd also highly recommend UW Atmospheric Sciences professor Cliff Mass' book "The Weather of the Pacific Northwest. A great read to learn about our local weather patterns.
If you're a fan of the USA Today weather page, they also have a good book "The Weather Book: An Easy-to-Understand Guide to the USA's Weather".
The current edition of the Farmer's Almanac makes a great stocking stuffer.
As a fan of weather photography, I always ask for a weather calendar. I'm partial to the annual one by Accord Publishing but there are plenty of other great ones out there. If you've got someone into storm chasing, check out Warren Faidley.
You might think I'd suggest a snow globe, but really, how often does it snow in Seattle?
That was also the thought of the makers of "Rain Globe". Check this out:
Looking for something to wear? The UK version of our National Weather Service has partnered with clothing company Rapanui to offer some weather-related garb.
This site also has some weather-related items to wear.
Or, you can always give the gift of storminess as Germany allows you to buy naming rights to storms. You'd probably have to wait until 2013 as most are taken for now, but planting a seed...
What Not To Get
A humble suggestion: If your person is into weather, they probably already have a version of the "weather rock" or "weather stick" where it says stuff like "if it's wet, it's raining, if it's moving, it's windy", etc.
If you've come across any other great ideas on your own, feel free to post in the comments below (provided the recipient won't recognize you :) )