Can anyone tell me if this one will work? and if there is anything else i need to buy to attach it to my gun?

WHYTELYTE SUB-COMPACT FLASHLIGH - LaserLyte

The only light that attaches directely to the Sigma's proprietary rail is the Insight M4 which is sadly out of production. But you may be able to get a used one on GB or ebay.

OR

You could use an adaptor like this one to convert to a standard 1913 picatinny and use a universal light.
LaserLyte Rail Adapter Smith & Wesson Sigma Matte - MidwayUSA

If you are going the adaptor route, I would recommend the Streamlight TRL-1 personally. Its a great light, well made and has a lifetime warranty and is only about $20 more than the laserlyte which looks cheap to me.

thanks. something like this ? INSIGHT REMOTE X-SERIES M4/M16 - eBay (item 140361642684 end time Dec-21-09 19:47:02 PST)

how about this one
FLASHLIGHT FOR S&W SIGMA 9VE 40VE QUICK RELEASE

The first link is for the remote switch, not the entire light.

I would stay away from the second one, unless you are just going to use it to mess around with. If you are going to be depending on your pistol and light for a potential life or death situation, it does not pay to go cheap.

I would get the adaptor:
Laserlyte Rail Adapter For Smith & Wesson Sigma Series 05945. ADPSIGM140. LaserLyte Laser Sight Accessories.
and this light:
Streamlight TLR-1 Rail-Mounted Tactical Flashlight FREE UPS Streamlight TLR1 Weapon Tactical Flashlight C4 LED 69110 69111 69112

with the link that you posted is there any modifying or is it direct bolt on

The adaptor is a direct bolt on.

sweet. thanks for the help. Ill go that route. I agree cheaper isnt always better. im going to sell the laser and get that.

No problem.

I think you will be very happy with the TLR-1. Its a great light that is quite nearly the equal of other lights costing 2+ times more.

Anyone ever wondered why a new gun from S&W has a rail that it does and not a picatinny rail?

New molds are expensive. The enhanced sigma was designed in a time when universal rails were not standard fare. Hell rails at all weren't standard for a few more years.

Now its one thing for a budget $300 pistol to have outdated proprietary rails, but why does a $1000+ HK USP have them ?

will this one work? it says it fits any rail

streamlight tlr1 tlr-1 c4 led - eBay (item 180441555772 end time Dec-07-09 19:59:37 PST)

No. The light in question has different plates to allow it to adapt to Picatinny or Weaver, and it can fit the S&W 3rd Gen rail, which has a shorter distance from the cross slot to the frame. The SIGMA does not use either of these systems and instead is more similar to an HK USP, which does not use a cross slot and which uses a clamp on arrangement. The SIGMA rail is proprietary and it never caught on. You will have to either use a light for the SIGMA (Insight M4, if you can find one), or get a rail adapter to change the S&W SIGMA to a weaver or picatinny type, then you can use a light designed for it.

The Picatinny rail has wider cross slots and the Weaver type has narrower cross slots. The Glock rail is the same as Weaver.

Didn't we already go over this ? Lol.

As long as you have the adaptor, yes it will work. That is a TLR-1 like i suggested.

what do you think of the tlr-3?

Advantages ?
Small, made for sub-compact pistols.

A little cheaper.

Disadvantages:

Not as bright.

Less run time.

Made of plastic instead of metal.

If you were looking for a light to stick on a M&P9C i would say go for it. But on a full sized pistol, i just don't see why you would want it. Save $20 for all the disadvantages ? I wouldn't.