As an avid Android user and proponent, I've found quite a few awesome apps for use to help me log my exercise.

Namely I've been using GPS based tracking applications while I either inline skate or cycle in my neighborhood. These applications do a number of things which I find useful for my purposes.
GPS Tracking allows for the following:
Most of these applications include the option to upload your logging to a web site as an option to either share your tracks or as an option to back up the data. If you chose to share the data, you can usually share it with your friends on Facebook and Twitter. Some of these sites even have community forums where you can share your experiences, help motivate each other, and participate in challenges.
What I love about this? It's motivating. While that may sound silly, when you take a look at how far you've traveled over all time, it's extremely motivating. At times I may feel like it's just not worth it, like I've not accomplished anything at all, or like I'm not getting anywhere with it. All it takes for me, is a quick glance at my history and before I know it I'm either suiting up to go ride or I'm eagerly looking forward to my next opportunity to do so.
On top of all of this, I love the fact that I can use my Motorola wireless head phones and the music from my phone or an online streaming radio station, all at the same time that the GPS logging application is running. No need to carry around a separate GPS tracking device along with a different MP3 player.
Recently I've wanted to find a Bluetooth Heart Rate Monitor (HRM) to help me with my training. There's many reasons to use a HRM in training. If you're not sure why that is, I'd suggest a quick Google search for more info. There's plenty of research out there to support their use.
In my searching, I've found the following device: Zephyr HxM

There are coupons all over the place for $5 off, making this device $95 + shipping. Not a bad price, especially when you consider everything you can do once you integrate it with the free applications out there.
Nice, but who are these people? Apparently, they've recently decided to enter the consumer market from their focus markets of military, police, and medical. Impressive to say the least. These guys will no doubt build a quality product! I decided to try and find a review of the chest strap and HRM since I've never worn one before and I'm not sure what to expect. Entering a search into Google and clicking on the first return, I came upon the following review: Running Digital Zephyr HxM Review
Very, very nice review! I guess I can quit worrying about how the chest strap will feel. That's nice to know. Apparently I can also rest assured that the product is a quality unit.
Now the real question: What applications are out there that utilize this thing and are they accurate and do they track what I'm interested in?
Initially I had been using Cardio Trainer, from WorkSmart Labs. It's a great application and it's what initially got me started on this whole kick to be honest. However, as of this writing, they didn't offer HRM integration with any product, not just the Zephyr. I started to want more though. Since I've wanted to take my training to the next level, I started to look into HRM integration. A quick Android market search for Zephyr HxM yields Endomondo and SportsTrack Live immediately. I'll provide what experiences I have with Endomondo as I've not had a chance to use SportsTrack Live extensively yet.
Endomondo appears to be one of the most well thought out, well developed applications and web sites I've come across thus far. One of the first things I noticed was the ability to import my workout history from CardioTrainer. Since you can import history from a Garmin or via a .GPX or .TCX file, you should be able to easily make the transition to Endomondo from just about any application on the market. Once I imported my data via the website, I noticed that there's a calendar that shows when I've worked out. Talk about a motivator! Being able to look back at my history and realize that I've stuck to my goals or that I've strayed from them makes a difference. The application allows me to specify what type of exercise I'm participating in, and it will automatically determine the start time of my workout, the total distance and duration of the average speed, max speed, an estimate of calories burned, a high and low altitude, and if I have it, my heart rate as obtained from the Zephyr HxM monitor.
Another feature I absolutely can't get enough of is the Google map overlay with each 'split' broken down. You can select how long these splits are. In my instance, I have the splits set for 1 mile increments. The Google map overlay displays the splits, as well as what time in your workout that split took place. This is really nice to know when you're concerned with maintaining a consistant pace for endurance training or if you're just interested in having a ton of data because you're a data junkie.
Endomondo also allows the ability to integrate with the media player on your phone. The application will list your playlist for your workout, how cool is that!? What's neat about this integration is that it doesn't just list your playlist, it tells you what song you were listening to at each split. This will allow you to know what specific song you were listening to when you notice that peek speed in the speed graph. Like the results? Maybe you should look at adjusting your music selection!
One more note: Endomondo, like many other sites, incorporates a user community to help in finding exercise buddies as well as helping to find ideas for routes and other motivational factors. You can search for friends, create teams, look for routes, join challenges, and even give live pep-talks to your friends that are out exercising! Now that's a cool feature!

SportsTrackLive is another site that appears to be extremely well thought out. However, at $9.95, I haven't forked over the money just yet to gain full access. Reading the reviews of this application though, I'm fairly interested! Perhaps I'll have more to come in the future on this application.