The Cook Political Report (subscription req'd) has looked at 30 congressional races and upgraded them for the Democratic Party. Many of these races are in heavily entrenched Republican areas, but it's clear that the prevailing attitude towards the GOP and the great work these Democratic candidates have been doing (often with help from the netroots) has put a whole bunch more of the House in play:

AL-03 Mike Rogers Solid Republican to Likely Republican
CA-46 Dana Rohrabacher Solid Republican to Likely Republican
FL-08 Ric Keller Likely Republican to Lean Republican
FL-09 Gus Bilirakis Solid Republican to Likely Republican
FL-18 Ileana Ros-Lehtinen Solid Republican to Likely Republican
FL-21 Lincoln Diaz-Balart Likely Republican to Lean Republican
ID-01 Bill Sali Solid Republican to Likely Republican
IN-03 Mark Souder Solid Republican to Likely Republican
IA-04 Tom Latham Solid Republican to Likely Republican
KY-02 OPEN (Lewis) Solid Republican to Likely Republican
MN-02 John Kline Solid Republican to Likely Republican
NE-02 Lee Terry Solid Republican to Likely Republican
NV-02 Dean Heller Solid Republican to Likely Republican
NJ-05 Scott Garrett Solid Republican to Likely Republican
NY-13 OPEN (Fossella) Toss Up to Lean Democratic
NY-25 OPEN (Walsh) Toss Up to Lean Democratic
NC-10 Patrick McHenry Solid Republican to Likely Republican
OH-07 OPEN (Hobson) Solid Republican to Likely Republican
PA-03 Phil English Likely Republican to Lean Republican
PA-05 OPEN (Peterson) Solid Republican to Likely Republican
PA-11 Paul Kanjorksi Likely Democratic to Lean Democratic
PA-15 Charlie Dent Solid Republican to Likely Republican
TX-07 John Culberson Solid Republican to Likely Republican
TX-10 Michael McCaul Solid Republican to Likely Republican
VA-05 Virgil Goode Solid Republican to Likely Republican
VA-10 Frank Wolf Solid Republican to Likely Republican
WV-02 Shelley Moore Capito Likely Republican to Lean Republican
WY-AL OPEN (Cubin) Solid Republican to Likely Republican