Unfortunately, I have recently faced the same problem, hoping that MS would provide a new version of Visio Enterprise Architect since I have used it FOREVER to do ERDs/database design. Since this does not seem to be forthcoming from them however, I have been forced to research other tools. The ones I checked out included the following:
- Embarcadero ER/Studio
- Visual Paradigm DB Visual Architect
- Altova DatabaseSpy
- Dezign for Databases
- Sybase PowerDesigner
Also, I tried to check out DevGEMS Data Modeler but kept getting "the setup files are corrupted" after downloading it. I never considered ERWin as the interface seems too old school/legacy plus it is too expensive. Just when I had almost given up all hope of finding a well-rounded but [relatively] cheap alternative I came across ModelRight. I find it curious that I haven't heard more about this company given that their product is EXCELLENT and inexpensive (under $1000 for multi-DB support or under $500 for a single DB type) compared to other high-end DB modeling tools. Further, the company was founded by one of the first developers to work on ERwin (see their company's "About" page for more info).
To make a long story short, if you want to save yourself a day's worth of research on this subject, check out ModelRight FIRST and go from there. BTW, for full disclosure - I have no affiliation with the ModelRight company! ;^)
P.S. - From what I can tell currently, VS 2010 isn't going to offer a full DB modeling environment but only enough to support the Entity Framework which I am not currently sold on (especially having spent the time to roll my own ORM layer).