I'm using my Playstation 3 on my Dell 2405 monitor but the problem is that certain games only support 720p.

The Dell 2405 has a native resolution of 1080p and it will accept and scale the 720p to 1080p but it looks absolutely horrible so I'm wondering what type of external scalers exist.

Keep in mind that the PS3 costs $400 so I can't justify spending $1000 on a scaler but I'm wondering if something cheaper exists that will look "decent". (eg. the X-Box 360 has a built-in scaler and it looks pretty good!)

I also need the scaler to not have much lag because of playing games.

I've seen a Gafen scaler for around $300 (still a bit pricey but maybe it's worth it?) that claims less than one frame of lag and it will upscale 720p to 1080i/1080p. Does anybody know anything about it?

Thanks for any help!

Basically none. Any of the inexpensive scalers (still more money than the PS3) are only going to marginally help. The Edge is probably the best canidate though if you really want to do it.