I'd like to monitor my podcasts with XLR-equipped audio monitors. Is there a sound card or a peripheral I should add to my Mac? I don't need input, as I"ll be working with digital files. Thanks.

you can use the audio outs from your mac with a 1/8" stereo to RCA X2 cable you can find just about anywhere. you could either change the ends to XLR, or go RCA->XLR adaptors. this will be an unbalanced connection. many speakers also have 1/4" inputs,and RCA->1/4" is a very common, cheap, easy to get adapter.

if you really need a balanced connection for a long run, you'll need a USB or FW audio interface. there are many basic units out there which are pretty cheap - under $200, which will also work. virtually all would give you mic level XLR ins too which could be handy.

I'd like to monitor my podcasts with XLR-equipped audio monitors. Is there a sound card or a peripheral I should add to my Mac? I don't need input, as I"ll be working with digital files. Thanks.

A "Y" adapter to take the 1/8 stereo Line Out from your Mac to 2 XLR connectors should be all you need

A "Y" adapter to take the 1/8 stereo Line Out from your Mac to 2 XLR connectors should be all you need
Here's a link to a picture of such a cable:
Y-Cable 1/8 (M) to Dual XLR (M) Stereo 6.6 Ft -  1/8 to XLR Cables- Balanced Cables- Cables, Snakes, & Adapters- Accessories- PSSL.com (http://www.pssl.com/!E3PqAjAe5-GY5VkrDg!n5w!/Y-Cable-18-M-to-Dual-XLR-M-Stereo-66-Ft)

Wow. I didn't realize an acceptable solution would be so cheap!