I have a .com domain that is expiring soon (in about a week). Can I renew my domain through a different company or is it stuck with my current registrar?
You can indeed renew a .com domain (and many others) through another registrar - it's basically just a normal transfer process.
Providing your domain name is not locked, you can transfer it to a new registrar now and pay for an additional year of registration at the same time (which you have to do when you transfer anyway).
Because transfers can take a couple of days to process though, if I were you I'd do this ASAP so your domain doesn't end up expiring in the process.
If your domain is locked at your current registrar, you'll need to unlock it by logging in to your registrar's control panel. You can also grab your authorization key (sometimes called an EPP key) at the same time, because you'll need that to initiate the transfer. While you're there also double check your registrant e-mail address is up-to-date, because you'll need to approve the transfer through there as well.
Checking each of these above items will ensure the transfer proceeds smoothly and in time. Once you've done this, initiate the transfer and renewal through your new registrar.