Bubbles

Note: that the background in the example image isn't part of this tutorial. You may use a solid color background, our any texture you'd like. To start off, take the Elliptical Marquee Tool and make a selection, hold Shift to make a perfect circle. Then, choose white as your foreground, and choose the Radial Gradient Tool (the Gradient Tool is hidden under the Paint Bucket in PS 7 and the radial gradient is the second gradient icon that appears on the top Options Bar) . Now click on the body of the large rectanglar gradient that appears on the Options Bar. Select the 'Foreground to Transparent' gradient. Then, apply the gradient to your circular selection. You might also want to lower the opacity of the layer a little (this can be done in the upper right corner of the Layers Palette).

With your selection still active, create a new layer, than go Edit>Stroke, make sure 'Inside' is selected and use a width of around 2-4 pixels. Now go Filter>Blur>Gaussian Blur with a setting of about 1-4 pixels, depending on how thick your stroke is. Then, adjust the opacity to match the rest of the bubble. You should have something like this.

And you're basically finished. You can easily duplicate your layer and scale it to different sizes by hitting Ctrl+T (Mac: Command+T) to create as many bubbles as you'd like!