Well, just to follow up, since you all were so good in sharing your thoughts and opinions on the matter... I've decided I probably ought to get a 220v machine to make sure I have sufficient power to weld the stuff I'm likely to be working with. I really would like to get a dual-voltage machine (e.g., Millermatic 211), but those are just too expensive for me at this time.
The likely prospects at this time are Lincoln Electric's Pro Mig 180 or Lincoln Electric WeldPak 180 (these are essentially the same welder, just badged differently for Lowes and Home Depot, respectively). It handles both MIG and flux-core welding, has a 30% duty cycle (more than enough for my needs), and it can even weld aluminum with an optional spool gun.
Other than a mask (auto-darkening, which I already have), welding gloves, a slag hammer and wire brush, can you think of anything else I might need to pick up?
Also, I'd like to find some steel to practice on; is there any typical places to find cheap pieces that I could play around with?