Advice/Suggestions for MacBook Pro Apps/Software

So I just bought a refurbed mid-2012 15 inch MacBook Pro with 2.3 GHz processor and 4 GB memory, and a GeForce 650M graphics card. Since my last Mac was a PowerBook G4 that ran Tiger and then Leopard, I am pretty out of the loop re new apps and software in general. It came with Mountain Lion but I installed Mavericks on it yesterday without incident.

I mainly use my laptop for coding, some simple graphics (I tried downloading GIMP yesterday but the installer wasn't recognised), and web surfing. I do a bit of gaming (would love to have the Sims 3 on it but am not terribly hopeful as Mountain Lion users reported problems with running it).

My question is, what apps/software would people recommend as 'essential' or 'good to have'? I'm not one for cluttering up memory with a lot of hardly-used apps, so want to stick to the mainly useful ones. I'm ignorant of apps since I was in the Dark Ages on the PowerBook till yesterday!

I put Text Wrangler on it, may upgrade to BBEdit since I used to run that in the past and liked it.

So.. any recommendations for 'must haves'?

I recommend Pixelmator over GIMP for user friendliness and over Photoshop for price. It's hard to beat free, I know, but just the sheer simplicity yet power of it makes the $15 a good spend. Couldn't tell you how it would run on Mavs, cuz I haven't upgraded yet. Great app, tho.