My "midi controller" is a Roland XP-10. It's done fine for me. Someone let me borrow it indefinitely. I think you can get them for about $40 on Ebay.
It has no control of VSTi's and such. Some instruments will let me cycle through the presets, however,
I've never used a real / nice midi controller. When I'm working it never really occurs to me that I need a better one.
As for your latency problem, try this first:
Home Recording Computers: Clicks, Pops, and Latency
Brandon