If you're an average shooter and just want to have fun and get some quality trigger time, any of your current guns will do just fine in Limited Class.
If you want to play with the big boys you'll need to upgrade. Limited gun of the moment is an STI of SV in 40 S&W. Unlimited would be STI or SV, compensated, optically sighted (C-More, Holosight etc) in 38 Super (some are trying the 9x23 but it hasn't caught on just yet).
Lots of IPSC members are selling Para Limiteds at some good prices - they are buying STI's and SV's.
I built an STI in 40 S&W for a combination IDPA/IPSC gun and couldn't be happier. I still like the single stacks but the fat gun is tops!