Here are some links to sites that I have found particularly helpful
Nibs.com - New fountain pens & nibs, nib customization and repair, fountain pen ink and accessories.
CSV Pens - Conway Stewart Vintage Pens. High quality Pens and Pencils at low prices.
David's Pen & Pencil Collection - Specialises in collecting Conway Stewart Pens and Pencils, plus other writing equipment.
Onoto Pen Company - Luxury limited edition fountain pens and writing accessories made in Britain since 1905.
Pens & Collectables - An extensive range of Fountain Pens, Pencils and Accessories, all fully serviced and guaranteed.
Sheaffer Targa Web Site - Specialist retailers focing opn Sheaffer Targa fountain pens and other Sheaffer models.
Writetime - several makes of vintage fountain pens and pencils, restored to full working order.
The Pen Practice - This site is devoted to the understanding and repair of vintage and classic fountain pens. I am no longer offering a repair service.
Vintage Fountain Pens - a huge collection of fine vintage fountain pen for sale, nibs, spares and associated inkwells, ink bottles and other pen related objects.
Writing Equipment Society - The history of writing equipment and the conservation of both utilitarian and fine items. Aids collectors to add to their collections through sales and exchanges.