A more advanced pen, than can easily be assembled by someone with intermediate/advanced skill. This project is still doable for someone with basic skill, just expect to make a few errors on the way.
http://www.wiimoteproject.com
http://bloglearningrhhs.blogspot.com
http://www.boonjin.com/wp
Parts:
Vishay TSAL6400 IR-Led: http://au.farnell.com/3152868/optoelectronics/product.us0?sku=vishay-tsal6400
AAA NIMH Battery, with tags: http://www.jaycar.com.au/productView.asp?ID=SB1724&CATID=18&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=583
SPDT Mini Micro Switch: http://www.dse.com.au/cgi-bin/dse.storefront/488201d1063a30ce273fc0a87f9c06b6/Product/View/P7802
Wire: http://www.dse.com.au/cgi-bin/dse.storefront/488201d1063a30ce273fc0a87f9c06b6/Product/View/W4010
Shrink Wrap: http://www.dse.com.au/cgi-bin/dse.storefront/488201d1063a30ce273fc0a87f9c06b6/Product/View/W4060
3.5mm Mono Socket: http://www.dse.com.au/cgi-bin/dse.storefront/488201d1063a30ce273fc0a87f9c06b6/Product/View/P1236
3.5mm Mono Plug: http://www.dse.com.au/cgi-bin/dse.storefront/488201d1063a30ce273fc0a87f9c06b6/Product/View/P1134
Alligator Clips: http://www.dse.com.au/cgi-bin/dse.storefront/488201d1063a30ce273fc0a87f9c06b6/Product/View/P6412 Less