This is the most general term I can think of. Hope it helps.

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Note added at 2004-07-10 00:59:39 (GMT)
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I found 310,000 hits on Google such as the following:
Letterhead Paper Preprinted letterhead paper for use in your inkjet printer, laser printer or copier. Order online from Icon Graphix.
www.icongraphix.com
Letterhead Paper at iPrint.com Free shipping when you spend $50 or more on professionally printed letterhead at iPrint.com. Design your own or choose from our vast design library. Corporate quality at low prices.
www.iprint.com
Granite Letterhead Paper 8 1/2 in. x11 in. Gray | Viking Office Products
Granite Letterhead Paper 8 1/2 in. x11 in. Gray - Get free Delivery for orders of $25 at Viking Office Products. Granite Letterhead Paper 8-1/2\'x11\' Gray at Viking Office Products
www.vikingop.com/catalogSku.aspx?ID=39872
Leaf Print Design Letterhead Paper
... Flower Dot, Foil Emboss Design Premium Letterhead Paper. Express your creativity ... Silver Swirl, Silver Foil Design Premium Letterhead Paper. Express your creativity ...
www.keysan.com/ksu0761c.htm - 68k - Cached - More pages from this site
Letterhead Paper on eBay
eBay offers great deals on items related to Letterhead Paper. ... Angel Letterhead Computer Paper Postcards 48, ends Jul-11 6:53 am PDT. ... 1893 Woodbury County, IA /(3) Letterhead Paper/ Letter, ends Jul-11 9:18 am PDT. ...
search-desc.ebay.com/search/search.dll?query=letterhead+paper&newu=1&krd=1
Letterhead Paper
Letterhead Paper. email letterhead. letterhead designs. printed business folders. cheap business cards. business cards online. unique business cards. Our Terms and Policies. How to send us a file. letterhead paper - ... Letterhead Paper. Home. View all products ... letterhead paper - Another important element of letterhead design is paper stock choice ...
www.letterhead.ws/letterhead-paper.html

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Note added at 2004-07-10 01:26:44 (GMT)
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My basis for this is pure grammar. \"Paper\" is the noun and \"Letterhead\" is the modifying descriptive adjective.

An even more generic possibility is: Letterhead stationery

I found 196,000 hits on google. Below is an example:

Create business cards, letterhead/stationery & envelopes easily
... how easy it is to design, preview and order custom printed. business cards, letterhead/stationery and envelopes online! ... clients demand. Letterhead/Stationery. DESIGN ONLINE! ...
www.printing2day.com/ - 43k - Cached

Again, \"Stationery\" is the noun and \"Letterhead\" is the adjective.
\"Papel Membretado\" in Spanish follows the same grammar guideline. \"Papel\" is the noun and \"Membretado\" is the descriptive adjective modifying the noun.

Membrete means the name, adress, and logo from somebody or some company... I see letter, or lettered head paper, in Simon's, but I'm not shure.
Luck.

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Note added at 9 mins (2004-07-10 00:51:05 GMT)
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That was it... letterhead, as Veronica says.