So I met with a trainer and he gave me info on how to monitor my heart rate during excercise. It really makes sense because I could really see when I was pushing myself too hard or not hard enough... They are super expensive! Do you use one?

I just bought one. Its an Omron 100C, I think. I got it on Amazon for about $35. It had good reviews and the chest strap is super comfortable on my rather large self.

ETA: It isn't super fancy and doesn't track calories burned or anything like that. Just the basics with an alarm you can set if you drop below or above a certain rate.

I have one, and it was an awesome investment of my money! Mine is a Nike Imara that I also got on Amazon for like $70. If you go to Amazon, do a search for Nike Imara Heart Rate monitor. The one I bought was light blue, I think that they only have a pink one out now. In any case, the one I have does track your calories burned during your workouts (I call it my "instant gratification monitor", the chest strap is very comfy, and the watch itself is very easy to use. You will see a lot of heart rate monitors out there that don't have chest straps, but the ones used with a chest strap are much more accurate for picking up your heart rate. I have also bought heart rate monitors in the past from Nashbar.com
Good luck in your search, and I definitely recommend that you invest in a heart rate monitor...

I have a Polar F4 Heart Rate Monitor and I love it. I got it as a Christmas gift from my boyfriend (as per my request--what a good boy ), but I know they run for about $90. It is--by far--the best little gadget I've ever had for weight loss and motivation at the gym.

It tells you your heart rate and calories burned (based on your HR, age, height, weight and gender)--and it's SO useful! In the grand scheme of things, spending $90 on a quality piece of fitness equipment that keeps you motivated and lasts for years is definitely worth it. I've spent more money on videos, books and magazines over the years that did me little good, than a HRM costs.

You should get one--I promise it'll be your new favorite toy (I've had mine for 1.5 years and it's MY favorite toy still for fitness!).

I use one for running an mountain biking. Nothing fancy, just a $19.95 jobbie (wrist unit w/chest strap) that I bought from Nashbar.com. I've had the same one for about 7 or 8 years. Very comfy and it works great! I love to get the the calorie count at the end of a workout...

My trainer has also been bugging me to get one for a long time, so I finally got a Polar F11. I LOVE it!! It took a little while to figure out all the programs, and I actually don't use them all. It's made me work out harder.

I've had a Polar F4 for about a month now. I LOVE it. It definitely keeps me more on track and I'm getting more out of my workouts because I'm always striving to stay above those flashing numbers! Definitely a great investment for me.

I have the Polar F4. My mum got it for me in February and surprised me with it when I came home (gotta love moms...haha). It's fantastic. I absolutely love it. It's great for when I do circuit training because I know when my heart rate drops too low. It's also great motivation; if I'm on the treadmill and am at 457 calories it's like "okay, just get to 500 before you get off". It also has a function so I can see how many hours I've worked out total (I reset it every week). Great toy. I would highly recommend one.

Another happy F4 owner over here. I love it and fit it to be a great motivational tool.