What you need
Photoshop


So you wanna make an awesome comic, eh? And you got the layout nailed, and your story is brilliant. One problem: you have no clue how to make good speech bubbles.

Well, let's not settle at good; how about excellent?

So you've got your scene down (hopefully it doesn't look like this) and now you want dialogue? OK. Let's go.

Type your text

Now, take the ellipse tool and draw a circle around it

OK, now get the direct selection tool out and click on the circles

See those squares? Click and drag them until you get a square-circle shape.

Good job. Now, create a new layer and place it under the text layer. Then, with the direct selection tool still out, right click your bubble and click ‘fill path’. Choose what color you want (normally white).

Now, take out the pen tool and click three times; first inside the circle, then outside the circle (where you want the tail to end; normally NOT right inside the mouth of your character) and then once again inside the circle, across from the first click.

Next, click the lines inside the circle and twist them both around until you get a good-looking curved bubble (sometimes when the lines you are dragging go outside the bubble the tail can get messed up; use caution and keep that history window open). Also, it helps to zoom in and do it for precision.

Select the empty layer you created earlier. Now, right click the tail and click ‘Fill subpath’. Choose the same color as before (again, normally white).

There! Now for the final touch: that empty layer you created earlier, make sure it's selected: now, double click it inside the layers palette to bring up the Blending Options window. Go to stroke and check the box by clicking it. Choose black and an inside stroke of ‘2’ and then click ‘ok’.

Finally, right click (direct selection tool!) the bubble and go to ‘delete path’.

There! The perfect speechbubble. Obviously you can use other effects, like a drop shadow or a glow, along with text and bubble effects. Once you have this technique down, experiment; the wonderful ting about photoshop is it's not chemistry; you can screw around with stuff and get great results.