Master Lock's Python cable lock boasts a neat ratchet mechanism that allows you to adjust the cable length from 30cm to 1.8m, and cuts out excess cable that could be easily snipped. Unfortunately what remains is easily snipped, making the Python hard to recommend.
The entry price point for proper U-locks seems to get lower every year, and this unit from Master Lock at £30 (less online) is a great piece of entry level security, resisting attack with the tenacity of steel costing twice as much.
The Street Fortum is well constructed from hardened steel, with a shackle that goes right through the locking bar helping to anchor it in place. It's finished in orange plastic and frame-friendly rubber, and you get four keys and a fairly bog-standard frame mount that does the job without any fuss.