I'm using
Palringo. Until this week it was completely free. There are now some premium features that you can pay for. (not sure how much yet, it'll be a week or 2 before they have the premium account up.) I'm fine just using the free features though. It loads automatically so your always online, if you want to be. Doesn't show in the task manager unless you have chats open. Memory usage is low just make sure you turn off the gps tracking function or it will drain the battery pretty bad. Give it a try, it's worth the 2 min to download and check out.