Yep, welcome along JML!
Given your question is fairly open, you will receive a lot of responses from different members as to what type of airbrush you should go for.
I'm no expert, so I'll leave it up to others to give advice, but for what it's worth, i'll tell you what i model and what i use - that way if your interests are similar, you will have some guidance.
I build 1/72 & 1/48 aircraft - mainly modern jets and WWII.
I'm also venturing into 1/35 armour.
The airbrushes i use are a Paashe H (as per Bill's recommendation above) and a Badger 100LG.
The Paasche H was my first airbrush and was great to learn with, however, it's now really relegated to when i need large surface coverage, eg priming, single colour schemes and gloss/matte coating.
I use the 100LG for pretty much everything else and really love it.
My main issue was i had trouble mottling Luftwaffe aircraft with the Paasche H (not saying you can't use it for that, just my skills weren't good enough to do so), so, I went out and bought a 100LG.
To be honest, I think the two together cover almost all my needs. (Though that doesn't mean i won't buy another airbrush one day).
Anyhow, most modelers have their preferred brands and models when it comes to airbrushes, so, perhaps if you let us all know a bit more about what you model/are interested in modelling, others might be able to help narrow down your search and/or steer you in the right direction.
Chris.