^ 555 features:
velocity sensitive pads
dedicated pattern copy
loop recorder
more banks for samples
d-beam
can be a MIDI controller AND soundcard

The SP-404 can't copy patterns? I don't care about the rest really.

Would it be a good idea to buy a Mini Kaoss Pad too or will I be sattisfied with SP-404's effects?

yeah it does have Pattern Copy but it's a little trickier than on a 555

the 404's effects are great, but i don't know what you're after
maybe try them both in store before buying to see whether its effects appeal to you

Can you only use the effects live or can you save them in your samples too?

I hear it doesn't save the BPM settings, isn't that really annoying?

yes you can save the effects to the samples. You achieve that with the resample button.

The BPM thing does get annoying, but I either write it down, or using the voice recorder, sample myself saying what bpm it is, and add that into the pattern, then when I am tracking, just mute that pad.

Thanks for the useful replies everyone!

One last question: is there an easy way to connect both my Kaossilator and DS-10 to the SP-404?

Just wanted to mention, picking the 555 over the 404 loses one of the best fx, vinyl sim compression, and battery power.

Ok thanks, I'm getting the SP-404 tommorrow. Just 2 more questions:

1) What's an cheap and easy way to connect the Kaossilator and DS-10 at once? Would a cheap analog mixer suffice?
2) Is there much of a difference between standard and lo-fi? I'm pretty sure the DS-10 is lo-fi on its own, I'll be content if the SP's lo-fi sounds the same.

you can put one in the RCA inputs of the 404 and the other in thew Mic input (but would only be mono after that)
so you may not need a mixer at all

I don't have one yet, it was too buzy in the store and it closed earlier than I expected. I really need to test it out before buying.

I'm just wondering if the SP-404 would still suffice if I bought a Microkorg or Waldorf Blofeld in the future. Or would the SP-404 become too limited?

What kind of synth you buy really does'nt have anything to do with workflow. If you dig the 404 flow what difference does it make where you get your sounds. It has its own flow, maybe you like it maybe you don't, but what you're using as input doesn't enter into the equation IMO.

What I meant is will I still be happy with the SP-404 or will I definately want something better?

I just don't see what that has to do with what synth you buy.

No, I'm just talking about expanding with another synth (doesn't matter which one). I was wondering if I will still be satisfied with the SP-404 when I get better, or will want something with more possibilities.

I don't think anyone can really answer that. You've got a lot of talented heads on this forum who either use or used and have much respect for the 404. It's just a personal question and I don't think you'll know until you get there. Not to bring this up again, but Madlib's a very talented producer and he made Madvilliany entirely with a 303, which is technically more limited than the 404. Just depends on you and the way you work, which you won't know until you've been at it a while. Anyway at $400 brand new the stakes are much lower investment-wise than say copping an MPC, JJOS and a new set of pads. =) The SP line is just about the cheapest way to get into non Fruity Loops based production.