I posted a thread like this a while back, more along the lines of putting together a bio for a press pack. Got a lot of good input, and settled on something like this;
http://xush.net/analog_missionary_bio.htm
We have a longer one with full press reviews and interviews, and a shorter one for sending to venues, etc. This is just the general format of the content- I'd use a spiffed up version with more graphics for printing/mailing.
When I send a pack out, I include at least the 2 pg bio w/ press excerpts, CDs, photo sheet, business card (good to send your contact info in at least 2 different printed forms- then they can't lose track of you) and maybe some promotional swag like stickers or whatnot...
I've recently been throwing in a handwritten postcard catered to the reason for sending the pack, and I've found that personal touch has really been making a difference lately.
People really respond to it.
It's good to make the envelope stand out from your average manilla affair too; every little bit that differentiates your band can make a bigger impact. Maybe a use colored envelope, or print some pics or logos or something on it.
I always try to think in terms of what would make me say "wow! Cool kit, these guys must be pretty interesting" if someone sent me a kit. And don't skimp, make it look as pro as possible.