I've always considered myself a pretty athletic person, but I recently had a big lifestyle change that caused me to gain some weight. I'm back down to around 150 lbs (I'm 5'5), and I'm working out quite a lot, but I've plateaued with my weight loss, so does anyone have any advice on how to beat it?
Here's what I'm doing now.

Daily bike commute: 9 miles roundtrip
Running 5 miles 3x per week TWF
Weight training 1 hr 3x per week WFSu
Kick boxing 2x per week R,Sa
This isn't a super regimented routine, and I usually take Mondays off.

Well first of all, what are you calling a "plateau"? Some people don't lose anything for 1-2 weeks and start thinking they've plateaued. You can't really know that you've hit a plateau until it's been several weeks (and I'd say around 6ish or more) w/out any significant weight loss.

Next, you're doing a huge amount of exercise, but you don't say anything about what you're eating. Diet is even more important than exercise ... and especially when you're doing that much. It's possible that you're not eating enough to suport the amount of energy you're expending and you've put yourself into a stall that way.

I've been at the same weight for about 4-5 weeks. I don't keep an exact count of how many calories I eat per day. Generally, I just try to make good choices, eat lots of raw veggies, lean meat, whole grains, etc. That doesn't mean I don't ever fulfill my serious cravings for sweets (maybe once a week?). It hadn't occurred to me that I may be exercising too much for the amount I'm eating. I feel pretty great, though. I thought I'd feel tired or sick if I was expending too much energy

Well given that you're not keeping track of what you're eating, it's possible that you might be eating too many calories, especially if you're having sweets once in a while.

I'd say that you should start tracking your food - use a site like livestrong.com (the daily plate or fitday.com or one of those. Until you KNOW what you're eating, any thoughts about why you're not losing are guesses at best.

Okay, so after a few days of keeping track of what I eat, Id say I average anywhere from 1500 to 2000 calories a day. The daily plate kinda keeps a "net calories" running total. For my weight, it says I should be eating 1500 calories/day. Does that mean net calories? I'm not in the practice of eating more just because I burned more calories. Could that be the problem?

Well according to my calculations, based on your weight of 150, you need to be eating around 1500-1700 calories to lose (depending on how active you are). 2250 is your maintenance figure. (Keeping in mind that all calorie calculations are estimates.)

If your diet fluctuates that much (and especially if you're not being really precise about measuring your food) it's entirely possible that you're simply eating too much. Honestly that would be my best guess.

You are doing a lot of working out, but I personally don't get quite so detailed as gross calories vs. net calories and all of that on daily plate. I just use it to track my overall calorie intake and my macros. I aim for about a 30% calorie reduction from my maintenance figure and then count calories burned exercising as a nice bonus.

I suspect that you simply need to be more careful and consistent with your eating for a while. Make sure that you measure (and weigh, where you can) what you're eating. And try to stick to between 1500 and 1700 calories per day.