There aren't many PDAs on the market with no phone built in. Palm makes most of the ones sold in the US, but HP does offer a few. They just released the iPAQ 111 recently, and that's a very nice model with a color display for $299. We'll be posting a review soon, but in the meantime, you can check it out on HP's web site: http://www.shopping.hp.com/product/handheld/PC/1/storefronts/FA979AA%2523ABA .
If you want to get a used one for less money, then look for an HP or a Dell model. Toshiba stopped making them quite some time ago, and the used ones are pretty old. Sony's PDAs run Palm OS and I'm not sure if you didn't want the Palm brand or Palm OS in general.