Feel free to add your favorites.  Here are some to consider.

Applied Information Science
Modeling Methodologies
http://www.aisintl.com/case/method.html

Booch Method
The Booch method covers the analysis- and design phases of a OO-system.
http://www.hsr.ch/div/Booch/BoochReference/reference.html

BroadVision
BroadVision One-To-One LiveCycle is a multi-disciplinary process that integrates business, content management, and creative and technical expertise to take your site live efficiently. Search for Methodology under Services
http://www.broadvision.com

Commen Sense
Commen Sense Approach to Project Planning and Managment plus link to software development methodology
http://members.home.net/ucconcepts/methodology.htm

Data Preparation Workbook
Planetary Data System (PDS)
http://pds.jpl.nasa.gov/dpw/

DisCo Specification Method
A specification method for reactive systems
http://www.cs.tut.fi/laitos/DisCo/DisCo-english.fm.html

ECAT's Standard Development Methodology
Electronic Catalog Corporation (ECAT)'s preferred approach to system development is to establish a number of interim milestones
http://www.ecatcorp.com/method.html

EROOS: Entity-Relationship OO Specs
An object oriented software development method
http://www.cs.kuleuven.ac.be/cwis/research/som/publications/CW208-E.shtml

JAD/RAD Process
Joint Application Development (JAD) is used as a technique for gathering business software requirements
http://www.piersonapp.com/methodology.html

LUCID Framework
LUCID is organized into six groups of activities, spanning the standard project management stages of a project:
http://www.cognetics.com/lucid/lucid.html

Microsoft Solutions Framework
Teaches Best Practices for Project Management
http://www.microsoft.com/business/services/mcsmsf.asp

Object-Oriented Hypermedia Design Model (OOHDM)
In OOHDM, a hypermedia application is built in a four-step process supporting an incremental or prototype process model
http://www.telemidia.puc-rio.br/oohdm/oohdm.html

PROCESS ENGINEERING METHODOLOGY
(PEM) defines a structured approach to process specification and automation
http://source.asset.com/Boeing/rde/pem/pem.htm

SEI Software Engineering Process Management Program
In 1993, the SEI released the Capability Maturity Model® for Software (SW-CMM®).
http://www.sei.cmu.edu/organization/programs/sepm/process.html

SUMMIT Ascendantä World-Class IT Process Management
SUMMIT Ascendant is PricewaterhouseCoopers' flexible, pragmatic and proven approach to systems delivery and IT project management
http://www.summitcoe.com

The Shlaer-Mellor Method
A well-defined [1, 2, 3] and disciplined approach to the development of industrial-grade software.
http://www.projtech.com/info/smmethod.html

Trology FCT™ Methodology
Trilogy Fast Cycle Time™ ("FCT™") methodology is a powerful new way for Global 2000 companies to deliver e-business project
http://www.trilogy.com/Sections/Industries/Financial_Services/Fast_Cycle_Time.cfm

Unified Modeling Language™ (UML)
Rational's industry-standard language for specifying, visualizing, constructing, and documenting the artifacts of software systems
http://www.rational.com/uml/index.jsp

University of California, Davis
Application Development Methodology
http://sysdev.ucdavis.edu/WEBADM/document/toc.html

University of Waterloo -- Waterloo, Ontario, Canada
Information Systems and Technology - Project Templates
http://ist.uwaterloo.ca/projects/templates.html

VBM - Methodology Reference
Containing the Full Scale Components of the VBM - Vision Based Methodology™
http://www.geocities.com/~itmweb/method.htm

Windward Methodologies
Methodology to deliver consumer and enterprise solutions that combine handheld, mobile, wireless, desktop, Internet, synchronization, server and database technologies
http://www.wwg.com/index.asp?index=7

I would also throw in:

A gentle introduction into XP (eXtreme Programming)

http://www.extremeprogramming.org/

Any ideas on methodologies that work well in small engineering design firms?  I come from a software development background.  Your list is quite comprehensive.

We focus on Front-End Engineering and Design and Conceptual work in the upstream O&G industry. 

I am trying to get the company a little more focused and increase productivity, consistency, and quality across the business. 

 Thanks

By the way...

 Don't forget PSP and TSP...

http://www.sei.cmu.edu/tsp/psp.html 

http://www.sei.cmu.edu/tsp/tsp.html

There are more methodolgies on the web than you will ever be able to digest or use.  I have seen companies operating at a good level of project implementation go to a poor or bad level by trying to adopt a methodology.  The most import thing to do is develop a methodology to handle the type of work your team does in an efficient manner.

My suggestion is to start with the top level of your WBS and brainstorm with some of your project leaders what needs to occur, what check points make sense, and what critical deliverables should be completed during your stages.  Don't overcomplicate your methodology.  Make it the lowest common denominator across your project types. 

I will attach a sheet I have used to help define my methodology over the years.  This can be modified/refined to match your needs.  Pay attention to the success factors to be able to tell your team what "Good" looks like.  The most important focus of a methodology should be project delivery, not stopping project progress to ensure you have all the i's dotted and t's crossed.