For a serious musician, amps are a very specific and personal thing. A lot depends on what he intends to use it for (hobby vs. pro), the type of music he plays, and the sound he wants to get. Very similar-looking amps can have very different sounds and features, even the same brand. Fender and Marshall are both excellent brands, but come in a wide variety of models.
You are correct that all-in-ones are called "combos." They come in a lot of different sizes, powers (tube, solid state, transtube) and all with different effects selections and speaker sizes. Most serious musicians like to try playing through prospective amps with their own guitar before making a selection. If you still want to surpise him, buy through a reputable dealer and make sure they have a solid return policy in case it's not what he wants. And, don't take it personally if he doesn't like what you bought him. A lot of musicians don't know what they want themselves.