Welcome to the site - do a little searching around and you'll find all the information you need.
But to give a quick and simple answer, there isn't much to do with our cars thus far for more power other than intake/exhaust/weight reduction/etc., and they don't really help much anyway. There is a supercharger kit available, but I hear the cost / benefit ratio isn't that great.
Good luck and welcome aboard....
You're looking around $6000 for the LMS supercharger kit and gaining about 40 hp at the wheels, which is pretty poor bang/buck.
Sadly the same is true for nearly all the mods available on the IS350...
There's full exhausts (not street legal) that can add 15 or so hp for a bit north of $1000... and there's axle-back exhausts (just about all of em street legal) that add more like 5-7 horsepower and cost in the 500-800 buck range.
There are intakes ranging from just over $100 (joe Z) to almost $500 (lexus f-sport) and most of them (just about ALL of em but the two I mention) are likely to lose you power since they're hot air intakes... the Joe Z is gonna be your best bang/buck and still only give you maybe 5 hp.
and... that's about it.
There's a couple of headers that aren't actually designed for the 350 but will technically fit, nobody really knows what gains if any they provide, but they're expensive
You could put nitrous on the car, the one guy I know who is running a 65 shot is actually getting fantastic results that are easily the best bang for the buck by a wide margin. Only downside is the risks of nitrous on a $10,000 engine that's still under warranty.
Nobody makes a chip (that actually does anything useful) for the 2IS.
Yeah, you might can get the shortblock for $3500, this assumes you didn't hurt anything else in the process that needs replacing, and can do all your own labor for a motor swap of course... and then you still have a stock motor that already blew up once with the system on it... so a lot more if you want a -built- motor... still probably a lot better off just buying an IS-F if you -have- to have an extra 100 hp.
The only thing that looks decent at this time are the Mazurri headers, which have just been completed. They're predicting an approximate 30hp gain for $650. If it's true, and they can correct the CEL, I'm saving my pennies!
Yeah, performance wise other than the Joe Z pipe the mazzuri headers are the first thing I've seen for the IS350 that isn't completely crap from a cost-per-horsepower standpoint.
Some warning though-
Performance is still unknown right now- Daniel is predicting 30 horsepower, which'd be great if true, but nobody knows yet. With a little patience I'm sure he'll provide some 350 testing before too long.
Your check engine light'll be on all the time- this is a fairly significant problem, but hopefully they'll figure a solution.
You'll miserably fail any sort of emissions inspection since it deletes the primary cats- this may or may not matter to you depending where you live, although it's technically illegal in all 50 states. You may or may not be able to get an exhaust shop to under-the-table make you something to add in that'll pass emissions, but YMMV.