I've used a 8mm Fisheye for a while and it was excellent for a first follow cam lens. It's not too expensive (about 200$ less than the 11-16 and 17-50) and I was able to use it with an Opteka handle and a cheap polaroid rig. The results were real nice for rails and small jumps, I've only had problem with bigger jumps (thats where the glidecam would've make a serious difference).
I'm thinking about getting a 12-24 soon, but I'll still use the fisheye alot. If you want to invest more a glidecam and a more expensive lens clearly is an excellent setup, but if you have a budget more similar to mine (student budget) a fisheye and a less expensive handle is a great way to start for under 400$.