Woah, loving those 150x40px graphix, might make one of my own!
I personally really like 100x30 and 50x50 images that a lot of fanlistings use, because they're easy to put into a nice looking grid. Also there's enough detail in the image so the image doesn't look blurry or compressed.
I think it'd be great to have all different sizes for link buttons, but it's also nice to have a standard. However, there's nothing stopping us from making a standard of multiple standards!
What if everyone used either 88x31 and 150x40, or maybe 176x50 to make it align better with an 88x31, so that the width is exactly double/half one another? Wouldn't that be cool?