Lowest latency soundcard to plug in guitar and play with software effects

Question

Hi,
I know latency is very often discussed, but i am finding it harder to find an answer to what i am looking for. I have a Mac Book Pro and so need an external sound card. I assume firewire is the way to go and firewire 800 should give the lowest latency.
I plan to plug in the guitar directly and then load on software effects. I am switching over from a pc and also haven't made music for a few years so i will have to buy the software modules - probably something like the latest version of amplitube (only because i used the old version 5 years ago and it was great). Then add some etc. delays or limiters etc.
Initially i will use just garageband, but plan to move on to either logic or pro tools if i get back into it properly. Initially, i just want to play along with other songs, but get great real-time effects (as close to as possible). Put it all through headphones and play along etc.
I want to get a sound card that gives me a very low latency (i assume that means going to rme or motu- both of which are very expensive.) I actually am unlikely to use more than 4 ins/outs. Anyone know of a website that actually lists latency or have any real values or other advice. I am not interested in direct monitoring.
Price i am willing to pay is still very variable - if i have to go to one that costs about $2000, then i will save up and wait, but they have so many features i will never touch. Don't play in a band and will never need most of those ins or outs.
The presonus firebox gets mentioned, but i think that is firewire 400 and i am not sure if it's latency is low enough.
Thanks for any help. I am using leopard in case that changes anything.

Answer 1

So to confirm, if i plug a clean electric guitar into the motu ultralite and put it through effects (on either garageband, logic, amplitube etc...), and listen to it post effects, i shouldn't notice too much latency - hopefully close to none at all (i know there is always some latency, but if i can't tell- i don't care).
I might be misunderstanding you, but I thought I'd chime in and clarify a couple of things that sound like you might be misunderstanding slightly. If not, I apologize!
Latency is only a factor when you're recording, not when you're playing stuff back. When you're actually recording into Logic, and trying to play along with a click or a drum track, and even though you're playing at the right time, you're hearing it late and/or it's recording late, that's latency. Most of the time when you're experiencing that, it's not about the interface that you're using (not always, but most of the time), but rather about the effects that you're trying to use when recording. If you're trying to play along to drums, and you have a bunch of processor heavy plug-ins on your project going, you might have to bump up the buffer setting, and that may introduce latency. The key is to keep your effects to a reasonable number when recording, so as to set the buffer low and latency will be manageable. Once you've recorded your guitar, then you can put effects and plugs to your hearts content, increase the buffer size, and everything will play in time. If you really push it, you might cause the audio to drop out, but with what you're doing your machine is plenty fast.
A good interface is always good, and I encourage you to get the best one you can afford (I love my Ultralite!) but it's more about how processor heavy the project is when you're recording. Once tracks are recorded, latency ceases to become a factor.
Get the MOTU, it's a great piece. And don't worry about latency, because you can always disable plugs while recording if they're causing problems, and then put them back once the track is recorded.
On another note, Amplitube 2 is a very nice guitar sim, I think it sounds great. And a lot of people actually like Guitar Amp Pro too, which comes with Logic. You've got options.
Good Luck!