Shimano CS-HG61 29er Cassette
This is the first cassette drop from Shimano that's been designated as 29er specific. The magic ingredient for 29ers is the 36 tooth cog which gives you that boost you've been lacking since you've made the jump to world of big wheels. Don't worry you weren't getting slow. Big wheels just accelerate a little slower, especially going uphill.
This cassette is optimized to work with Shimano's M529 and M629 29er specific hubs but will work just fine with anything that's Shimano compatible.
The 36t large cog was exactly what I needed on my 29er. It gave me that lower gear that all my friends have with their 26" wheels for the steep, loose climbs. Shifts smoothly with my X-7 derailleur. I've punished it for a full season and it is holding up well. A bit on the heavy side, but an excellent value.