Dollar Cost Averaging vs. Lump Sum Investing
DCA advocates will tell you to dollar cost average everything. If you come into a lump sum, you should spread these purchases out over several months. Honestly, though, you can make up sotck purchase prices to support either side - DCA or lump sum purchases.
Research usually shows that it doesn't matter in the long term; here's the latest research I've seen on the subject.
The bottom line:
1. If you're currently doing dollar cost averaging, that's great. Don't stop.
2. If you have a lump sum to invest, don't worry about dollar cost averaging. Make the purchase with the entire lump sum. DCA and lump sum purchases will give approximately equivalent results.