Museum Quality Framing does an excellent job of custom framing. I've had at least 10 prints framed by MQF in the past 2 years, and I've been completely satisfied each time. The employees are very helpful with mat and frame recommendations, and the turn-around time for a framed piece is usually just 10 days (even during the busy holiday season). They have a good selection of mat colors, frame styles and glass options.
They offer a full-satisfaction guarantee, and they live up to it! When one of my prints slipped out of its mount, MQF repaired it for no charge.
Custom framing is generally expensive, and MQF is no exception. However, they frequently have sales events (i.e. 20% off) and mail coupons to frequent buyers. Look for discounts on their website (www.mqf.com), ValuPak mailings, and the Entertainment Book.