I use a digital Kearsarge 301; it's industrial-strength, bulletproof etc, $249.95 at B&H. Yes there are cheaper with more features, but this thing was used daily at a pro lab before I got ahold of it maybe 10 years ago, and I think it's got a couple hundred thousand more miles in it.

Otherwise, I'd be strongly inclined to consider an RH Designs Stopclock www.rhdesigns.co.uk/ since I print with the f-stop timing method anyway.