Birthday Party Invitations - Nashua,NH

I am in the midst of planning my son's 1st birthday party -- and had the same problem... I ended up going to www.vistaprint.com and ordered the flat invitations (they come with envelopes and don't require extra postage or anything).
You can pick from different templates and personalize them to say whatever you want with different fonts & colors. I even added a picture of my son to the front of our invites.
If you decide to use vistaprint, sign up for their emails first before you order anything. I get emails just about every day from them that include offers of free stuff and super discounted items... you may be able to get a really good deal on them.
Also, you can try googling "vistaprint discount codes" for other offers that may be out there.
I spent only $30 for 90 invites. Considering how much standard invites (the ones you have to fill-out yourself) cost at a party store - and you only get between 8-10 in a package, I think this was a really good price.
I have a huuuuuge family - so we needed that many, but you can order as few as 10.
Good luck!

Go to zazzle.com. They have every invitation imaginable and you can customize it to your needs. Prices are reasonable and they ship quick. They also run specials like discounts on custom t-shirts, posters, Christmas cards, etc. so sign up for their email reminders and you might catch a day where they're running a special on their invites. I've made custom t-shirts for Xmas gifts that were a huge hit with my teenage son and his friends as well as luau invitations for my parents 50th wedding anniversary.

I think most people simply pick their party theme and send invitations that go with that (spiderman, mario...whatever it happens to be). We had a friend who made hers on the computer and wrote something along the lines "Hip Hip Hooray! It's my birthday. Come jump, tumble and play. It's X's 4th birthday!". Another option would be to google bounce house invitations. I'm sure you can find several people who make and sell them.

You could try tinynotes.com or design your own and have a bunch printed out.